The permissible pH values for public water supplies is in the range 

Concept:

• The pH value of water indicates the logarithm of the reciprocal of hydrogen ion concentration present in water. It is thus an indicator of the acidity or the alkalinity of water.
• Hence, if the pH of water is more than 7, it will be alkaline, and if it is less than 7, it will be acidic. The maximum acidity will be at zero value of pH and maximum alkalinity will be at a value of pH equal to 14.
• pH is measured by potentiometer in which potential exerted by H+ is measured.
• It can also be measured by colour indicator. Colour formed is compared with standard colour.
• Permissible limit: For drinking water, permissible limit of pH is 7 to 8.5, but it should not be less than 6.5 and not greater than 9.2, hence Permissible values of pH for public supplies may range between 6.6 to 8.5.