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Your Disinfection Team: Chlorine and pH

Note: A PDF version of this document is available; this HTML page contains the same information as that found within the PDF: Your Disinfection Team: Chlorine and pH Fact Sheet [PDF - 102 kb].

Protecting swimmers and their families from recreational water illnesses (RWIs) is the reason that pool staff regularly check both chlorine and pH levels. Chlorine and pH, your disinfection team, are the first defense against germs that can make swimmers sick.

What does chlorine do?

Chlorine kills germs in pools--but it takes time to work. Therefore, it’s important to make sure chlorine levels are always at the levels recommended by the health department (usually between 1.0 - 3.0 ppm).

Why does chlorine need to be tested regularly?

All sorts of things can reduce chlorine levels in pool water. Some examples are sunlight, dirt, debris, and material from swimmers' bodies. That’s why chlorine levels must be routinely measured. However, the time it takes for chlorine to work is also affected by the other member of the disinfection team, pH.

Why is pH important?

Two reasons. First, the germ-killing power of chlorine varies with pH level. As pH goes up, the ability of chlorine to kill germs goes down. Second, a swimmer’s body has a pH between 7.2 and 7.8, so if the pool water isn’t kept in this range then swimmers will start to feel irritation of their eyes and skin. Keeping the pH in this range will balance chlorine’s germ-killing power while minimizing skin and eye irritation.

What else can be done to promote Healthy Swimming?

The best way to kill germs is by routinely measuring and adjusting both chlorine and pH levels. Since a few germs can survive for long periods in even the best maintained pools, it is also important that swimmers become aware of Healthy Swimming behaviors (don’t swim when ill with diarrhea, don’t swallow pool water, take frequent bathroom breaks, and practice good hygiene). Combining Healthy Swimming behaviors with good chlorine and pH control will reduce the spread of RWIs.

Relationship between pH and Water Quality
Water Quality	pH
- Poor Chlorine Disinfection - Eye Irritation - Skin Irritation	> 8.0
- Most Ideal for Eye Comfort and Disinfection	7.8 7.6 7.2
- Eye Irritation - Skin Irritation - Pipe Corrosion	< 7.0