Swimming Pools

The degree of acidity or alkalinity (sometimes called basicity) of a water is measured in terms of its pH value. A pH value of 7 is neutral; a value falling below 7 indicates an increasing degree of acidity; rising above 7 indicates an increasing degree of alkalinity. As pH value is measured on a logarithmic scale, each unit up or down represent a tenfold difference in alkinity/acidity.

Adjustment of the pH value of pool water is essential.

The bactericidal action of most disinfectants depends on pH, and it is therefore necessary to maintain the pH value within the optimum effective range for each disinfectant.
For example, the bactericidal efficacy of chlorination decreases rapidly as the pH value rises towards 8.
As the pH value rises towards 8, the water also has an increasing tendency to encourage precipitation of hardness salts.
As the pH value falls below 7, the water becomes increasingly corrosive to pool materials.
if the pH value is too low or too high, the water can irritate the skin and eyes.
Coagulants are significantly less effective if the pH value goes above the recommended range.
Residual analysis needs a steady pH.

These factors suggest different pH values, so there is no ideal value, but an optimum for each disinfection system. In practice, it is sufficient to keep the pH value within a range for each disinfectant. Operators using clorine-based disinfectants should aim for the bottom of the recommended range (7.2-7.4 better than 7.2-7.8) where disinfection is most effective. If lowering the pH is followed by worsening water quality, clearly some other action must be taken.

Environmental Health Officers have the authority to monitor water quality in swimming pools.

This page was last updated on 7/29/2008