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That “Chemical Smell” at the Pool Isn’t What You Think It Is

For America’s Most Fun Form of Summer Exercise, Experts Urge Swimmers to Use Senses to Stay Healthy at the Pool

As Americans jump into another fun-filled summer of swimming, a new survey finds that most don’t know the real reason why some pools have a strong chemical smell. A survey conducted on behalf of the Water Quality and Health Council found that three-quarters of Americans incorrectly believe that the chemical odor they smell at pools is a sign that there’s too much chlorine in the water.

Experts at the Water Quality and Health Council, U.S. Centers for Disease Control and Prevention (CDC), and the National Swimming Pool Foundation® (NSPF®) said properly treated swimming pools do not have a strong chemical smell. However, when chlorine in pool water combines with pee, poop, sweat, and dirt from swimmers’ bodies, chemical irritants called chloramines1 are produced. These chloramines give off a chemical odor, cause eyes to get red and sting, and use up the chlorine, meaning there is less to kill germs.

“It’s understandable why most people think that a chemical smell means there is too much chlorine in the pool, but the truth could be the opposite,” said Chris Wiant, Chair of the Water Quality and Health Council. “To help prevent chloramines from forming where you swim, shower before swimming and take little swimmers on regular bathroom breaks.”

Experts from the Water Quality and Health Council, CDC, and the NSPF are advising swimmers to use a “Sensible Checklist” to ensure a fun and healthy swimming experience:

  • Are the pH and chlorine level correct? Use a test strip to check.
  • Standing at the edge of the pool, can you see the drain in the bottom of the deep end?
  • Do drain covers on the bottom of the pool appear to be secure and in good repair?
  • Is a lifeguard on duty? If a lifeguard is not on duty, is safety equipment (for example, a rescue ring or pole) available?
  • Is the area around the pool free of strong chemical odors?

“Swimming is proof that exercise can be fun if you just add water,” said Thomas M. Lachocki, Ph. D., CEO of NSPF. “It’s not just a form of fun exercise though. Swimming is a lifetime survival skill. Learning to swim should become a priority for all parents and adults, not only could their children become healthier for it, but they could also save someone’s life someday.”

Getting the Word Out

The Water Quality and Health Council is once again making free test kits available this summer through their Healthy Pools campaign. Swimmers can test their backyard or community pool to ensure it has proper pH and chlorine level. To order a free test kit offered as part of the Water Quality and Health Council’s award winning summer Healthy Pools campaign, please go to www.healthypools.org.

The National Swimming Pool Foundation would like to encourage adults to find swimming classes for themselves and their children through swimtoday.org. Learning to swim today, can improve your health and save a life tomorrow.

To learn more about healthy and safe swimming, check out CDC’s new Healthy Swimming website at www.cdc.gov/healthyswimming.

The survey was conducted online by Survata, an independent research firm in San Francisco. Survata interviewed 1,500 adults May 12-13, 2016 and has a margin of error of 2.5%.

1 These chloramines are different from the type of chloramine that is sometimes used to treat drinking water.

2 The survey was conducted by Survata, an independent research firm in San Francisco. Survata interviewed 1,500 online respondents between (TBD) and (TBD). The margin of error for the survey is 2.53%.

Lifecycle of the Zika-transmitting Mosquito

Mosquito borne illnesses have played a significant role the course of human history and continue to have repercussions on human health. The World Health Organization (WHO) calls the mosquito the “greatest menace” of all disease-transmitting insects, responsible for several million deaths and hundreds of millions of cases every year.  Malaria alone, transmitted by Anopheles mosquitoes, caused 438,000 deaths in 2015 and sickened 214 million people globally, according to the World Malaria Report (2015).  Historically, it was “a leading obstacle to Africa’s colonization,” note the authors of a National Academies Press book on the

Four stages in the life cycle of mosquitoes Image courtesy of the US Centers for Disease Control & Prevention website

economics of malaria drugs.1 “It struck US presidents from Washington to Lincoln, weakened Civil War soldiers by the hundreds of thousands…traveled to California with the Gold Rush and claimed Native American lives across the continent.”2

The Aedes aegypti mosquito transmits a host of illnesses, from Zika virus and yellow fever to dengue and chikungunya.  The YouTube video and photo above clearly illustrate the four life stages of the Aedes aegypti mosquito, from eggs to adults.  Understanding the Aedes aegypti mosquito life cycle is key to understanding how to control it.

The “Container-breeding Mosquito”

Standing water is the perfect environment for mosquito breeding because it is where the larvae develop.  As summer approaches and Zika virus transmission risk rises, health officials are asking the public to remove even small amounts of standing water.  According to a US Centers for Disease Control and Prevention (CDC) blog, the Aedes aegypti mosquito “likes to lay eggs in water that collects or is stored in manmade containers.”

A Multi-front Defense
Besides removing standing water, shore up your defenses against mosquitoes this summer by using a CDC-approved insecticide, such as DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol. Lightweight, long-sleeved shirts and long pants also can help protect you from mosquito bites, particularly while spending extended periods of time outdoors. Finally, be sure that window and door screens are in good repair.

We recommend dumping standing water after no more than two days from 3:


Pet Water Bowls



Pool and Boat Covers


Uncovered Trash Cans/Indented Lids

Rain Barrels


Garden Ornaments that Collect Water


Other Mosquito Control Strategies

The Mosquito Control Association recommends changing the water in birdbaths and wading pools at least once per week, and stocking ornamental pools with “top feeding predacious minnows,” which eat mosquito larvae.  Alternatively, ornamental pools may be treated with biorational larvicides (active against a given target, but relatively innocuous to non-target organisms), or S-methoprene-containing (insect growth regulators) products.  Chlorine solutions are also known to inhibit mosquito larvae development, probably through an insect growth regulator mechanism.  Research is being conducted to determine effective solution concentrations.

Discarded tires can be a mosquito breeding paradise.  Avoid storing these outdoors, but if no other options are available, these can be treated with a larvicide.


Additional Tips for backyard swimming pool owners:

  • Empty the water from small inflatable and molded plastic kiddie pools immediately after use.
  • Keep larger pools properly chlorinated to inhibit mosquito breeding. Leaving to go on vacation?  See to it that the pool is treated while you are away, or cover the pool.


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1 Institute of Medicine (US) Committee on the Economics of Antimalarial Drugs; Arrow KJ, Panosian C, Gelband H, editors. Washington (DC): National Academies Press (US); 2004. On line, available:  http://www.ncbi.nlm.nih.gov/books/NBK215638/

2 Ibid.

3 Based on the CDC blog, “Zika Virus:  Zika, Mosquitoes, and Standing Water,” posted March 22, 2016.  Online, available:  http://blogs.cdc.gov/publichealthmatters/2016/03/zikaandwater/

Preparing for the Summer of Zika Virus

Fig. 1. U.S. map showing 1) Ae. aegypti potential abundance for Jan/July (colored circles), 2) approximate maximum known range of Ae. aegypti (shaded regions) and Ae. albopictus (gray dashed lines), and 3) monthly average number arrivals to the U.S. by air and land from countries on the CDC Zika travel advisory. Additional details can be found in the text. Figure reproduced with permission of PLOS Currents Outbreaks.


Are you curious about your risk of contracting Zika virus this summer?  The figure above is from a brand new study1 on the projected spread of the Aedes aegypti mosquito, the main Zika virus “vector”2. Based on meteorological models, mosquito-breeding patterns, air travel and socioeconomic status, the study compares the January, 2016 abundance of the mosquito (upper hemisphere of each circle) in each geographical location with its projected abundance this July (lower hemisphere of each circle).  The area of each circle is proportional to the estimated monthly average arrivals of people to the US from countries on the Centers for Disease Control and Prevention (CDC) travel advisory list.

The researchers project the greatest concentration of the Aedes aegypti mosquito in the US this summer will be throughout the Gulf Coast states and along the eastern seaboard as far north as New York City, a destination of many arrivals from countries on the CDC Zika travel advisory.  In fact, the circle for New York City is approximately the same size as the one for Miami.

Zika Virus to Date

As of early spring, 2016, virtually all of the known Zika virus infections in the US have been acquired during travel to other countries. Many Zika-infected individuals travelled to Latin America and the Caribbean, where there are Zika virus pandemics.  In Florida, where I am an Environmental Administrator in the Florida Department of Health (FL DOH), we have documented 67 cases of travel-related Zika virus.  Texas has had 27 confirmed cases, including one believed to have been sexually transmitted.  With the northern migration of the Aedes aegypti mosquito carrier this summer, however, Zika virus could soon be transmitted in the US.

The FL DOH and other state and county health departments in Zika virus-vulnerable areas are in full response mode.  States of emergency have been declared in 12 Florida counties,3 and Florida has a mosquito control district operating in every county. Having worked at the FL DOH for over 30 years, I know we will harness the lessons learned in the past fighting other mosquito borne illnesses, such as Eastern Equine Encephalitis and Dengue Fever.  We will inevitably learn a few new tricks as we turn our attention to Zika.  We already have a robust communication plan around this public health threat.

What Florida is Doing to Fight Zika

Daily Zika Updates:  Each day at 2 pm EDT, the Florida DOH issues an online Zika update and press release, identifying new Zika cases, making recommendations, and providing links to additional information.

Tips for Residents:  The Florida DOH website “encourages Florida residents and visitors to protect themselves from all mosquito borne illnesses by draining standing water; covering their skin with repellent and clothing; and covering windows with screens.”  See our “Drain and Cover” web page for more information, including keeping pool chemistry maintained.  Appropriate pH and chlorine levels will help avoid swimming pools becoming breeding grounds for mosquitoes.

Tips for Travelers:  The Florida DOH website advises travelers to tropical and sub-tropical regions can protect themselves from Zika virus and other mosquito borne illnesses by using appropriate insect repellent, covering skin with long-sleeved shirts and long pants, and keeping mosquitoes out of hotel rooms by choosing a hotel with air conditioning or window screens or sleeping under a mosquito bed net.  Our website notes that pregnant women should consider postponing travel to areas of Zika virus transmission.

Basic Information on Zika virus:  Zika is transmitted through the bite of infected Aedes aegypti mosquitoes. Perinatal (mother to child in the weeks just before or just after birth) and sexual transmission have also been reported.

 As summer approaches, stay tuned to public health communications on Zika virus so that you can make decisions and take actions to help protect your family.


Bob G. Vincent is an Environmental Administrator in the Florida Department of Health. He manages Department of Health programs for Healthy Marine Beaches, Safe Drinking Water, Water Well Surveillance and Public Pools and Bathing Places.

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1 Monaghan AJ, Morin CW, Steinhoff DF, Wilhelmi O, Hayden M, Quattrochi DA, Reiskind M, Lloyd AL, Smith K, Schmidt CA, Scalf PE, Ernst K. “On the Seasonal Occurrence and Abundance of the Zika Virus Vector Mosquito Aedes Aegypti in the Contiguous United States,” PLOS Currents Outbreaks. 2016 Mar 16 . Edition 1. doi: 10.1371/currents.outbreaks.50dfc7f46798675fc63e7d7da563da76.

2Disease vectors, according to the World Health Organization, are “living organisms that can transmit infectious diseases between humans or from animals to humans.”  In addition to Zika virus, the Aedes aegypti is a vector for Chikungunya, Dengue fever, Rift Valley fever and Yellow fever.

3 Alachua, Brevard, Broward, Hillsborough, Lee, Miami-Dade, Orange, Osceola, Polk, Santa Rosa, Seminole and St. Johns Counties

Zika Virus: On the Move

Zika virus is being actively transmitted by mosquitoes in Brazil, Paraguay, Bolivia, Ecuador, Columbia, Venezuela, Curacao, Guyana, French Guyana, Suriname, Mexico, Guatemala, Honduras, El Salvador, Nicaragua, Panama, Haiti, Dominican Republic, US Virgin Islands, St. Martin, Puerto Rico, Guadeloupe, Martinique and Barbados.

The Zika virus, a flavivirus1, is spreading “explosively” through several Latin American and Caribbean countries, according to the World Health Organization (WHO), prompting that group to declare an international health emergency which, according to the BBC “…means research and aid will be fast-tracked to tackle the infection.”  The virus is transmitted through the bite of the Aedes aegypti and Aedes albopictus mosquitoes, the same mosquito that, according to WHO, transmits dengue, chikungunya and yellow fever.  The virus was identified in the Zika forest of Uganda in 1947 in rhesus monkeys, then in humans in Uganda and the United Republic of Tanzania in 1952.  Recently, Zika virus was reported in Chile in 2014, followed by Brazil in 2015.  Currently the virus is being transmitted actively in over 20 countries.  As of yet, there is no reported active transmission of the virus in the US, but some travelers have returned to the US infected with Zika virus.  As CDC notes, “Any travelers visiting or returning to parts of the United States with established populations of Aedes aegypti or Aedes albopictus mosquitoes could initiate local virus transmission.”

Health Effects of Zika Virus

The Zika virus is spread mainly by the Aedes Aegypti mosquito. Mosquitoes breed in stagnant water and, unchlorinated pools and water storage tanks.

The US Centers for Disease Control and Prevention (CDC) notes that one in every five people infected with Zika virus will become sick for up to one week with fever, rash, joint pain and “nonpurulent” conjunctivitis (“pink eye” without the pus).  That means that 80 percent of people infected have no symptoms, but are carriers of the virus.

Zika virus testing is not widely available.  It is performed only at the CDC Arbovirus Diagnostic Laboratory and a few state health departments, according to CDC.  Test results can be misleading (false positive) if the individual in question was previously infected with another flavivirus, such as dengue, or has been vaccinated against yellow fever or Japanese encephalitis.

Pregnant women who are infected with the virus can pass it on to their unborn children.  There is a question, based on preliminary data from countries such as Brazil , as to whether those children may be at risk for microcephaly, a condition of abnormally small heads that is associated with underdevelopment of the brain.  Studies are needed to clarify whether there is an association between Zika virus infection and microcephaly and Guillain-Barre syndrome.

Pregnant women or women who may become pregnant should not travel to outbreak areas.  Meanwhile, the virus continues to spread at an alarming rate, and there is neither a vaccine for its prevention nor anti-viral medications for treating symptoms.   Research on Zika virus is just beginning, and new information will likely be revealed in the weeks and months ahead.

Maintain Chlorine Levels in Swimming Pools and Water Storage Tanks to Help Prevent Mosquito Breeding

Mosquitoes breed in standing water, not just the puddles and pools remaining following a rainstorm, but any still water that is not intentionally made inhospitable to breeding. For that reason, it is important to maintain appropriate chlorine levels in swimming pools and water storage tanks.

Swimming pool water should be chlorinated in the range of 1-4 parts per million (ppm) and stored drinking water chlorine levels should be kept above 1 ppm free chlorine. This measure not only helps prevent mosquito-breeding, but also helps prevent a host of waterborne illnesses that can be contracted from bacteria and other pathogens in water.

Preventing Zika Virus TransmissionStrategies to prevent mosquito breeding and human exposure to mosquitoes are our best bet for preventing the virus transmission.  These include:

  • Eliminating standing water in flower pots, buckets, barrels, old tires, untreated kiddie pools and other containers that can serve as breeding grounds for mosquitoes.
  • Ensuring good drainage of water around homes.
  • Maintaining a chlorine residual of about 1 mg/l in stored treated drinking water; drinking water storage is common in developing countries that lack central water distribution.
  • Making sure backyard pools are appropriately chlorinated as mosquitoes will not breed in chlorinated water.
  • Inspecting and repairing window and door screens.
  • Applying an insect repellent to exposed skin and/or clothing when spending time outdoors. The Aedes aegypti mosquito bites during daytime hours. Products containing DEET, picaridin, IR3535, and some products containing oil of lemon eucalyptus and para-menthane-diol may provide long-lasting protection; follow label directions for use.2
  • Applying insect repellent to skin after applying sunscreen, if sunscreen is to be used.
  • When you are outdoors, air movement around your body (from fans or natural breezes) disrupts mosquito flight and reduces your risk of being bitten.


Ralph Morris, MD, MPH, is a Physician and Preventive Medicine and Public Health official living in Bemidji, MN.

Fred M. Reiff, P.E., is a retired official from both the U.S. Public Health Service and the Pan American Health Organization, and lives in the Reno, Nevada area.
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1 Flaviviruses, according to CDC, are a family of positive, single-stranded, enveloped RNA viruses that cause widespread illness and death.  They are found primarily in ticks and mosquitoes and can occasionally infect humans.  Flaviviruses include Yellow Fever, Dengue Fever, Japanese encephalitis, West Nile viruses and Zika virus.

2 For more information on insect repellents and their effectiveness, please see http://cfpub.epa.gov/oppref/insect/.

This Winter, Use Your Senses around Your Indoor Pool

A “Natatorium” is an indoor swimming pool

Is swimming your exercise of choice this winter? According to the US Census Bureau, swimming is America’s fourth most popular recreational activity after (1) walking,
(2) exercising with equipment and (3) camping. Unless you’re a polar bear, indoor pools help make swimming a year-round option, and swimming brings health benefits galore. But how do you know if you are swimming in a healthy indoor pool?

The Water Quality & Health Council asks swimmers to be sensible around the pool. Translation: In addition to making smart decisions on safety, such as diving only in designated areas and not running on the deck, swimmers can use their five senses to:

  1. See: You should be able to see clearly through the water to the pool floor stripes.
  2. Smell: Indoor pools should not have a strong, irritating chemical odor. This is a common problem in indoor pools, however, stemming from (a) poor air ventilation and/or (b) improper pool chemistry. See the text box below.
  3. Touch: The tiles around the pool water line should feel clean, not slimy.
  4. Hear: You may hear the sound of the pool filter at work.
  5. Taste: Avoid tasting the water; swallowing even a small amount of water could make you sick. Remind children not to drink pool water!
Indoor Air Quality
Irritating chemical compounds called chloramines can build up in the air and water of an indoor swimming pool, causing respiratory and other health effects that degrade the indoor swimming experience. Chloramines are the chemical products of (a) chlorine from pool sanitizers and (b) ammonia-based substances (e.g., sweat, urine, oils) from the bodies of swimmers. Pool facility operators can minimize swimmers’ exposure to chloramines by maintaining proper pool chemistry, and encouraging swimmers to shower before entering the pool and refrain from “peeing in the pool.”

Another way that pool operators can reduce chloramines in and around the pool is by adequately managing air exchange in the indoor pool environment. Chloramines are volatile and fill the air over the swimming pool after they form in the water. Air currents that sweep away chloramines also help remove chloramines from the water. Good air exchange with outside air also helps reduce the humidity of the indoor air, helping to reduce mold and mildew.

Another way to ensure that you are swimming in a healthy pool is to use pool test strips to check that the pH and “free chlorine” level are within acceptable bounds. These strips are available in hardware and pool supply stores, and free from the Water Quality & Health Council each summer.

For more information on indoor pool air quality, please see the US Centers for Disease Control and Prevention website.

Bob G. Vincent is an Environmental Administrator in the Florida Department of Health. He manages Department of Health programs for Healthy Marine Beaches, Safe Drinking Water, Water Well Surveillance and Public Pools and Bathing Places.

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Responding to Dengue Fever

Responding to Dengue Fever

The female Aedes aegypti mosquito is the “vector” that transmits dengue fever from person to person.Image reprinted from the US Centers for Disease Control and Prevention website.

In the wake of recent monsoons and flooding, mosquito-borne dengue fever is once again on the rise in the Asia Pacific Region.  According to the US Centers for Disease Control and Prevention (CDC), worldwide, dengue fever cases number over 50 million annually.  The World Health Organization (WHO) estimates1 that globally 2.5 billion people, over one-third of the world’s population, live in areas that put them at risk for the viral disease, and about 70 percent of them (1.8 billion) live in the Asia Pacific Region.

Dengue is rare in the continental US, but endemic in Puerto Rico, where the CDC maintains a center of expertise and a diagnostic laboratory in its San Juan Dengue Branch.  It is also endemic to the Caribbean, Mexico and Central America.  According to the Gates Foundation website, dengue fever incidence has increased 30-fold worldwide since the 1960s.  Increasing urbanization and global travel contribute to ongoing outbreaks globally.

Dengue Fever Symptoms

Dengue fever symptoms range from mild fever to incapacitating high fever, with severe headache, pain behind the eyes, muscle and joint pain and rash, according to the World Health Organization.  Symptoms appear 3 -14 days after the infective bite.   The CDC advises patients to go immediately to an emergency room or closest health care provider if any of the following warning symptoms appear:

  • Severe abdominal pain or persistent vomiting
  • Red spots or patches on the skin
  • Bleeding from nose or gums
  • Vomiting blood
  • Black, tarry stools (feces, excrement)
  • Drowsiness or irritability
  • Pale, cold, or clammy skin
  • Difficulty breathing

Dengue hemorrhagic fever is a severe, potentially lethal form of the disease that generally requires hospitalization.  Children usually have a much milder form of dengue fever than adults, but those who survive the disease have a much greater chance of dengue hemorrhagic fever if they are subsequently infected as adults with a different serotype of the virus.

Avoiding Mosquitoes to Avoid Dengue Fever

Dengue fever is spread by the bite of infected Aedes aegypti mosquitoes, which are endemic to the southeast sector of the US among other world regions.  Humans are the reservoir of the disease, and there are at least four dengue viruses.  A person bitten by an infected mosquito may or may not develop symptoms.  That person cannot transmit the illness directly to others, but if a mosquito bites that person after he/she becomes infected, that mosquito can spread dengue fever to others through ongoing biting. According to the CDC, the Aedes aegypti bites primarily during the day. This species is most active for approximately two hours after sunrise and several hours before sunset, but it can bite at night in well-lit areas.

There is neither a vaccine for dengue fever nor specific antiviral medicines to treat the illness.  Preventing dengue is a matter of avoiding mosquitoes and their bites. Strategies include:

  • Eliminate standing water in flower pots, buckets, barrels, old tires, untreated kiddie pools and other containers that can serve as breeding grounds for mosquitoes.
  • Ensure good drainage of water around homes.
  • Maintain a chlorine residual of about 1 mg/l in stored treated drinking water; drinking water storage is common in developing countries that lack central water distribution.
  • Make sure backyard pools are appropriately chlorinated as mosquitoes will not breed in chlorinated water.
  • Inspect and repair window and door screens.
  • Apply an insect repellent to exposed skin and/or clothing when spending time outdoors. Products containing DEET, picaridin, IR3535, and some products containing oil of lemon eucalyptus and para-menthane-diol may provide long-lasting protectionfollow label directions for use.2
  • Apply insect repellent to skin after applying sunscreen, if sunscreen is to be used.
  • When you are outdoors, air movement around your body (from fans or natural breezes) disrupts mosquito flight and reduces your risk of being bitten.

The Indian Government is Activated

The Indian Express reports the current Dengue Fever outbreak is the worst one in five years, and notes other diseases with similar symptoms are also on the rise, including typhoid and B. coli.  The newspaper reports government inspectors go house-to-house in New Delhi in search of standing water, for even a few milliliters of clear water can become the breeding grounds of mosquitoes. Steep fines are imposed on residents who harbor standing water.  Fumigation is practiced in some areas.  Children are advised to wear full-sleeved shirts.

Government doctors have been told they will be on the job with no leave until the outbreak subsides and the number of hospital beds has been increased.

A High-opportunity Target

As flooding in the Asia Pacific region subsides, dengue cases are expected to decline.  Nevertheless, the disease remains one of the “most widespread vector-borne viral infections in the world,” according to the WHO.3  The Gates Foundation calls dengue fever a “high-opportunity target” because several potential vaccines are in development. The foundation supports efforts to develop a dengue vaccine, which it estimates could prevent more than 500,000 hospitalizations and 3,000 deaths annually, most of these among children (see press release).

An effective vaccine against dengue fever is the response we would most like to see to this global scourge.

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For more information on dengue fever and the Aedes aegypti mosquito, please see this CDC resource.

Ralph Morris, MD, MPH, is a Physician and Preventive Medicine and Public Health official living in Bemidji, MN.

1See: World Health Organization, Regional Office for South-East Asia, Asia-Pacific Dengue Strategic Plan (2008-2015)

2For more information on insect repellents and their effectiveness, please see http://cfpub.epa.gov/oppref/insect/.

3WHO.  Dengue hemorrhagic fever:   Diagnosis, treatment, prevention and control. Geneva. World Health Organization, (1997): 12-23

How to Drain a Residential Swimming Pool

Summer’s nearly over and many backyard swimming pool owners will soon undertake their annual “pool draining ritual.” Draining the water helps prevent damage to pools in geographic areas subject to freeze-thaw cycles. This article provides information to help you drain your pool responsibly.

What’s the Big Deal?

It’s easy enough to fill your pool with water, so why is draining it a big deal? First, all summer your swimming pool water has been treated with chemicals to help keep it safe for you and your family. Chlorine-based sanitizers, for example, probably were used to help destroy waterborne pathogens that can cause diarrhea, swimmer’s ear and skin infections. These germs can enter the pool on the bodies of swimmers and in animal feces. Chlorinated pools also prevent your backyard pool from becoming a mosquito breeding ground; mosquitoes potentially spread diseases like West Nile virus. But the same low levels of chlorine-based sanitizer that help keep pool water safe for your swimmers can be harmful to fish and wildlife.
The second reason to stop and think before you pull the plug is to consider the sheer volume of water and where it will flow to or pond outside the pool. Will it flow onto your neighbor’s property? Will it pond in a depression? Are you planning to drain your pool directly into a sewer? Better find out what type of sewers are nearby. A storm sewer will channel your pool water directly into a natural stream or other body of water with no treatment. Only sanitary sewers channel wastewater flow to treatment facilities.

This storm sewer in Montgomery County, Maryland bears a sign that indicates water flowing into it drains into Rock Creek, a tributary of the Potomac River, and warns residents not to pollute.

Tips to the Drainers

  • Consult your local municipal Department of Environment Quality for specific guidelines or codes. The US Environmental Protect Agency (EPA) website highlights, for example, Montgomery County, Maryland’s Department of Environmental Protection guidelines.
  • According to an Oregon Department of Environmental Quality Fact Sheet, if possible, swimming pool water should be sent to a treatment plant via a sanitary sewer. This is most important for large (especially community) pools, and happens automatically when in-ground pools are built with a drain that goes to a sanitary sewer.
  • If drainage to a sanitary sewer is not possible, water may be allowed to evaporate to a lower level for the winter, if desired, or disposed of on the ground or used to irrigate your property. Water should be released, however, only after the pool owner stops adding chlorine or other treatment chemicals, or shuts off the chlorination system and holds the water in the pool for at least one week while chlorine levels drop.
  • When disposing of pool water on the property or using it to irrigate your property, do so in a manner that water will not flow off your property or into a stream or storm sewer.
  • When disposing of pool water on your property, do so in a manner that water will not pond for a prolonged period, resulting in nuisances such as odors and insect breeding conditions.
  • If discharge to the ground will result in flow to a stream ditch or storm sewer, increase the holding time of water in the pool with no added chlorination to at least two weeks to allow chlorine to dissipate.
  • Use a pool test kit to measure the chlorine level of the pool water prior to draining to ensure there is no detectable chlorine level (for example, the Washington, DC Department of Energy and Environment website indicates less than 0.1 mg/l free chlorine is acceptable). A longer holding period may be necessary if free chlorine levels are above 0.1 mg/l.

Happy Swimming Pool Winterizing!

Chris Wiant, M.P.H., Ph.D., is president and CEO of the Caring for Colorado Foundation. He is also chair of the Water Quality & Health Council.

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West Nile Virus: A Seasonal Epidemic in North America

West Nile Virus Activity by State – United States, 2015 (as of August 11, 2015)
Map courtesy of the US Centers for Disease Control and Prevention

This summer North America is once again experiencing a “seasonal epidemic” of West Nile virus that is expected to last through the fall.  According to the Centers for Disease Control and Prevention (CDC) website, the mosquito-borne virus has been reported in 42 US states as of August 11, 2015.  Fortunately, most people who are infected with the virus show no symptoms; about 20 percent of people infected develop mild symptoms (e.g., headache, body aches, joint pains, vomiting, diarrhea or rash) after three to 14 days.  Less than one percent of those infected become seriously ill (e.g., high fever, muscle weakness, neck stiffness, stupor, and potentially permanent or fatal neurological disease).  There are no medications to treat West Nile virus, nor vaccines to prevent human infection1Avoiding West Nile virus is primarily a matter of avoiding mosquito bites.

West Nile Virus Transmission

According to the Centers for Disease Control and Prevention (CDC) website, the West Nile virus cycles between mosquitoes and birds.  Mosquitoes become infected with the virus by biting infected birds; they then pass the virus to humans and other mammals through mosquito bites.  West Nile virus is believed to have been in the US since about 1999 when it was first detected in New York City, but human infections have been reported in many countries for over 50 years.  According to the World Health Organization website, the virus is found in Africa, Europe, the Middle East and West Asia, in addition to North America.

West Nile virus can kill some host birds when the virus concentrates in their blood.  Sightings of multiple dead birds could be a sign that the virus is circulating in the vicinity.  CDC notes reporting dead birds to county and state health departments may be helpful to West Nile virus monitoring activities.  Additionally, some health departments monitor mosquitoes for the West Nile virus, which may be supplemented by monitoring sentinel chickens and dead birds.  According to the CDC report, “West Nile Virus in the United States:  Guidelines for Surveillance, Prevention, and Control,” “Research and operational experience shows that increases in WNV [West Nile virus] infection rates in mosquito populations can provide an indicator of developing outbreak conditions several weeks in advance of increases in human infections.”  (The report is linked to this CDC website.)

Reducing Your Risk of West Nile Virus is a Three Step Process

  • First, know your inherent risk level. People over 50 years of age have a greater chance of developing serious symptoms of West Nile virus than those younger than 50.
  • Second, know when to expect the “enemy.” Many mosquitoes are most active from dusk to dawn; these are the hours during which special precautions may be warranted, including avoiding being outdoors.
  • Third, take steps to avoid mosquitoes and their bites.
    • When outdoors, use effective insect repellents; those containing DEET,  picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products may provide longer-lasting protectionfollow label directions for use (For more information on insect repellents and their effectiveness, please see http://cfpub.epa.gov/oppref/insect/.)
    • Wear long sleeves and long pants of tightly woven fabric; tuck pant legs into socks for extra protection
    • Inspect and repair screens on windows and doors
    • Remove standing water in flower pots, buckets, barrels, old tires, untreated kiddie pools and other containers that can serve as breeding grounds for mosquitoes
    • Make sure backyard pools are appropriately chlorinated; mosquitoes will not breed in chlorinated water
    • When you are outdoors, air movement around your body (from fans or natural breezes) disrupts mosquito flight and reduces your risk of being bitten.

Your local health department may provide additional information about protecting against mosquito-borne diseases in your area.

What to do if You Think You Have West Nile Virus

According to CDC, mild symptoms of West Nile virus will improve on their own without medical intervention.  Severe West Nile virus symptoms may require hospitalization.  West Nile virus is not spread from casual human contact, such as touching or kissing.  If you have severe symptoms and think you may be infected with the West Nile virus, seek medical attention immediately.

For more information on West Nile virus, please see www.cdc.gov/westnile.

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Chris Wiant, M.P.H., Ph.D., is president and CEO of the Caring for Colorado Foundation. He is also chair of the Water Quality & Health Council.

*WNV human disease cases or presumptive viremic (“viremic” is defined as the presence of a virus in the blood) blood donors. Presumptive viremic blood donors have a positive screening test, which has not necessarily been confirmed

† WNV veterinary disease cases, or infections in mosquitoes, birds, or sentinel animals.

1According to the World Health Organization, vaccines are available for use in horses.


What to do about Bird (and Other) Droppings in the Swimming Pool

There’s nothing like a swim in an outdoor pool in beautiful summer weather. As the open air is the domain of nature’s flying creatures, however, the occasional splat of bird droppings in the pool is to be expected. What, if anything, needs to be done about bird droppings in the pool?

According to the US Centers for Disease Control and Prevention (CDC) website, many germs that might be present in bird droppings can infect humans, although few, if any, outbreaks have been associated with bird droppings. Duck and goose droppings are highlighted by CDC as potentially containing E. coli, Salmonella, Campylobacter or Cryptosporidium. Fortunately, in a well-maintained pool most pathogens in bird droppings are killed by chlorine within minutes, according to CDC. Cryptosporidium, a microscopic parasite surrounded by a tough chlorine-resistant outer shell, can be removed by a well-maintained pool filtration system.

Addressing Bird (and Other Types) of Droppings in the Pool

CDC recommends pool managers and backyard pool owners treat bird droppings in the pool in the same way that they would respond to finding formed human feces in the pool. The goal is to remove the waste material, if possible, and disinfect the water by taking the following steps:

  • Close the pool to swimmers.
  • Put on disposable gloves.
  • Remove the waste material using a net or bucket. Do not vacuum the waste from the pool.
  • Clean off any debris or dirt from the item used to remove the waste.
  • Disinfect the item used to remove the waste by immersing it in the pool during the 30-minute disinfection time described below.
  • Remove and dispose of gloves.
  • Wash your hands thoroughly with soap and water immediately.
  • Raise the free chlorine concentration to, or maintain it at, 2 parts per million (ppm); maintain the pH level at 7.5 or less; keep the temperature at 77°F (25°C) or higher. The free chlorine and pH should remain at these levels for 30 minutes.
  • Confirm that the filtration system is operating properly.

How to Discourage Birds around the Pool

CDC provides the following tips for discouraging birds (not the duck and geese varieties) from frequenting the pool area:

  • Remove plants that produce edible nuts, fruits, and berries.
  • Remove bird feeders.
  • Trim or remove trees and shrubs to limit branches hanging around or over the pool that can be used by roosting birds.

To discourage ducks and geese:

  • Do not keep domestic ducks and geese in the pool area to decrease the likelihood of wild ducks and geese becoming attracted to the area.
  • Do not feed ducks or geese.
  • Ducks and geese eat grass. If possible, reduce the area of grass lawns around the pool or install barriers that control movement between the pool and grass lawns, such as fences, grid wires and hedges. Noise makers, goose repellents and trained dogs can also be used to discourage non-migratory or resident geese from becoming a nuisance.

Happy swimming! For more information on addressing animals and pools, please see this CDC website. For further information on waste products in pools, please see the CDC’s Fecal Incident Response Recommendations for Pool Staff, linked from this CDC web page.

Bob G. Vincent is an Environmental Administrator in the Florida Department of Health. He manages Department of Health programs for Healthy Marine Beaches, Safe Drinking Water, Water Well Surveillance and Public Pools and Bathing Places.

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Avoiding Norovirus at the Lake

 Norovirus, the notorious “stomach bug,” can spread like wildfire  through homes, schools, healthcare facilities and cruise ships.  According to a recent report by the US Centers for Disease Control and Prevention (CDC), the virus also can be spread among swimmers in natural water bodies. In July, 2014, 70 people became ill with norovirus after swimming in Oregon’s Blue Lake, on the outskirts of Portland.  More than half of these were children between four and ten years old.  A CDC investigation found those who swam in the lake over the course of one weekend were more than twice as likely to develop vomiting or diarrhea as those who visited the lake but did not go in the water.  The outbreak was the subject of public communication during CDC’s 2015 Healthy and Safe Swimming Week1.

Anatomy of an Aqueous Outbreak

Last summer’s norovirus outbreak in Oregon probably started after a sick swimmer had diarrhea or vomited in the lake, dispersing numerous norovirus particles into the water.  Other swimmers then inadvertently swallowed water contaminated with norovirus. Unlike treated recreational water venues such as pools and water parks, natural waters do not contain disinfectants that can destroy norovirus and other pathogens.  Even in properly treated venues, however, disinfectants take time to work, so one should never assume pool water is completely germ-free.

Norovirus is the second-leading cause of waterborne illness outbreaks in untreated recreational waters. The leading cause is the bacterium Shigella.

Blue Lake was closed to swimmers for ten days to prevent further norovirus cases, but CDC noted its investigation highlighted a need for guidance for public officials to help them determine when to reopen recreational water venues following outbreaks.  We agree this should be a priority, especially given the fact, as CDC notes, that there is evidence norovirus can survive in water for several months, and even years.

Healthy and Safe Swimming

The CDC report also noted a need for communication tools to inform the public about the risks associated with swimming in untreated recreational water venues, including the ocean, lakes, ponds and rivers.  Many of the same tips for avoiding waterborne illness in treated venues, such as swimming pools, apply to lakes and ponds, including:

  • Don’t swim if you have diarrhea or have been vomiting.
  • Don’t urinate or defecate in the water.
  • Don’t swallow lake water.
  • Take children on frequent bathroom breaks.
  • Check diapers, and change them in a bathroom or diaper-changing area–to keep germs away from the water.

We submit the following additional tips for healthy swimming in untreated recreational water venues:

  • Do not swim in waters posted as “no swimming” zones.
  • Avoid swimming after a heavy rain to avoid exposure to sewage from overflowing sewage treatment systems or contaminated runoff.
  • Limit the amount of water going up your nose to reduce your chance of contracting a rare but deadly Naegleria fowleri amoeba infection. These infections have been documented in people who swim or dive in warm fresh water venues.
  • Check with local health or environmental officials if you are unsure about swimming in a natural body of water.
  • Shower after swimming.

For more information on swimming in natural water bodies, see the CDC website, Oceans, Lakes & Rivers and the linked US Environmental Protection Agency’s brochure, “Before You Go to the Beach” at:  http://www.cdc.gov/healthywater/swimming/oceans/.

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1 Formerly known as “Recreational Water Illness and Injury Prevention Week,” this year the annual observance occurred May 18-24, 2015.