Potential Hydrogen

Index to express the degree of acidity or alkalinity of a matter. A potential hydrogen (pH) is said "neutral" when it is equal to 7, "acid" when it is less than 7 and "alkaline" (or basic) when it is greater than 7. For drinking water, it must be greater than 6.5 units. Below this limit, the water is aggressive, with a corrosive effect on pipes, which may lead to the dissolution of toxic metals such as lead. The pH should be less than 9, the limit above which the water is too alkaline.