A Guide to Healthy Swimming: Understanding Causes of Pool Water Contamination

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For many, there is no better way to spend a hot summer day than relaxing by the pool. Public pools are favorite destinations for those looking to cool off, have fun, and spend quality time with family and friends.

Contracting water-borne illnesses is not top of mind when you are having fun. However, it is important to be aware that sharing the pool water with other people does come with risks.

Many blame symptoms such as upset stomach, diarrhea, and cramps on the food they ate, rather than the water they swam in.

Unfortunately, disease-causing microorganisms such as bacteria, viruses, and parasites can be present in pool water and spread from person to person through inhalation, touching or swallowing, causing unwanted illnesses.

Preventing water-borne illnesses has its challenges.

First, while water contamination can happen in minutes, the presence of harmful microorganisms cannot be detected without testing. Chlorine, the most commonly used pool sanitizer, is very effective in neutralizing most of contaminants. However some types of bacteria and parasites can still be active in the presence of chlorine for days.

Second, most prevention measures are beyond a person’s control, especially when using a public pool. In other words, you cannot easily spot people who are ill and prevent them from getting into the pool, or be completely certain that the pool maintenance crew has followed the recommended maintenance schedule.

Finally, there is no easy way to check if various pools components, such as pipes, air vents, filters and the area around the pool are maintained properly. We have to rely on the professionalism of those responsible for pool maintenance to keep us safe.

Most illnesses related to pool water are caused by bacteria, viruses and parasites.

Bacteria are single-cell organisms that can reproduce on their own, and are very resilient to extreme hot, cold, and radioactive environments.

The presence of bacteria is usually negatively perceived. In reality only about 1% of all bacteria are harmful.

The most common disease-causing bacteria present in pool water are Escherichia Coli (E-Coli), Pseudomonas aeruginoasa, and legionella.

Viruses are much smaller in size than bacteria and cannot survive and multiply in the absence of a host. While most bacteria are harmless, viruses are the cause of many diseases that affect various parts of the human body.

Parasites also use a host’s “resources” to survive and multiply. The word “parasite” derives from the Greek words para (meaning “alongside”), and sitos (meaning “food”). Some parasites, such as Crypto, are responsible for significant pool water infection outbreaks that sometimes affect hundreds of people.

The Invisible Dangers of Pool Water

Below are some examples of common and dangerous microorganisms that can cause serious illnesses, especially among people with vulnerable immune system, such as children and the elderly.

E-Coli is probably the most commonly known bacteria, responsible for many serious water-related illnesses and even deaths.

E-coli resides in the digestive systems of humans and animals, and is spread though fecal matter, especially by young children who are not potty trailed. Other sources of feces in water include drops from birds and animals, and cross contamination from other sources, such as dirty footwear.

People who swallow water contaminated with E-coli experience symptoms such as severe diarrhea, fever and abdominal cramps.

Pseudomonas aeruginoasa thrives particularly in warm water and can spread through the air, by contact with contaminated human skin, and feces. The main source of contamination is an already infected person that carries the bacteria into the pool water, thus contaminating others.

Symptoms include red itchy rash, conjunctivitis and sore throat and nausea, among others.

Legionella is another well-know bacteria that thrive in warm water and is responsible for Legionnaires disease. Legionella is spread through inhalation, and causes fever, abdominal pain, headaches, and weight loss. The most severe form of the disease is the Legionnaires disease (pneumonia).

Crypto is a dangerous parasite present in human and animal intestines and transmitted to other swimmers through feces. Swimmers who swallow contaminated water experience very unpleasant heath consequences, such as diarrhea, cramps and fever.

What makes Crypto very dangerous is its ability to survive for many days in water treated with chlorine. As a result, proper prevention measures are crucial to avoiding a Crypto outbreak.

As seen above, water-borne infections caused by bacteria, viruses and parasites share many similarities.

The main sources of contamination are sharing the pool water with people and pets already infected, human discharges (perspiration, feces, and urine) and touching contaminated surfaces such as beach chairs, towels, and toys. The symptoms can also be similar (headaches, cramps, fever, diarrhea), which makes the diagnostic challenging.

Do Your Part

Pool water safety is a shared responsibility. While we can’t control and influence other people’s decisions, actions and behaviors, we can certainly have an impact on our family’s and our own. Here are some small steps you can take to enjoy a safe day at the pool:

  • Avoid using the pool if you or your family members are sick.
  • Always shower thoroughly before entering the pool.
  • Never pee or poop in the swimming pool.
  • Ensure young children do not experience an accidental discharge in the pool.
  • Change baby’s diapers in designated areas, such as family washrooms.
  • Dispose of used diapers in appropriate garbage containers.
  • Make sure fecal matter is not present on your clothes and footwear.
  • Avoid sharing toys, beach towels and other objects with people around you.
  • Allow pets to swim only in the designated areas of the swimming pool.

Following these simple rules is a good step towards enjoying a hot summer day safely by the pool. You will not only protecting yourself and your family, but will also allow others to have a good time.


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