Recreational Facilities : Nova Scotia Labour and Advanced Education, Building and Equipment Safety

Protecting Against Recreational Water Illness

What is Recreational Water Illness?

Swimming pools can become contaminated by disease-causing microorganisms such as E.coli 0157.H7, Shigella, Giardia and Cryptosporidium. These microorganisms enter pool water through fecal matter and you can become sick if you accidently swallow contaminated water. This is known as recreational water illness or RWI.

The first defense against recreational water illness is maintaining proper chlorine and pH levels in the pool.

Why use chlorine?

Microorganisms that cause recreational water illnesses are killed by chlorine. Unfortunately, chlorine can take some time to kill the organisms. Cryptosporidium, for example, can live for days in a pool making it important to make sure chlorine residuals (levels) are maintained at levels recommended by the Department of Health-between 1.0 and 3.0 ppm.

Many things can affect chlorine levels in pool water such as sunlight, debris, dirt and fecal materiel from swimmers' bodies. That is why it is essential to routinely measure and record the chlorine residual in the pool at least four times a day* - optimally at the beginning of the day and after each swim event or activity.

Why is pH important?

Water Quality and pH
Water Quality pH
Poor Cl Disinfection
Eye Irritation
Skin Irritation
Most ideal for
Disinfection and
Eye Comfort
Eye Irritation
Skin Irritation
Pipe Corrosion

The amount of time it takes chlorine to work in a pool is also affected by the pH of the pool. The ability of chlorine to kill microorganisms varies with the pH. As the pH increases, the disinfectant ability of chlorine goes down.

Keeping pH in the 7.2 - 7.8 range (see chart) will maximize the chlorine disinfecting power as well as maintain swimmer comfort.

For instance, the pH of a swimmer's body is between 7.2 and 7.8 so if the pH of the pool is not within this range a swimmer may start to feel eye and skin irritation.

Can recreational water illnesses be prevented in other ways?

The best way to kill microorganisms in pool water is by measuring and adjusting the chlorine and pH. Unfortunately, even in the best maintained pools some organisms survive for a long time.

That's why it is especially important that patrons know what they should do to reduce the risk of recreational water illnesses. This include such things as not swimming when ill or have diarrhea, not swallowing pool water, taking frequent bathroom breaks, and practising good hygiene like washing their hands after using the toilet.

*The increased temperatures of spas and hot tubs can cause the chlorine to evaporate more quickly than in a swimming pool. Therefore, it is important to check and adjust the chlorine or other disinfectant level more often than pools.