Aqueous solutions have pH's, and the pH tells you (on a logarithmic scale) the concentration of H+ (or more preciselyH3O+) in that solution... the potential of Hydrogen.

pH is the single most important element in swimming pool water chemistry. It affects every other chemical balance in pool water.

pH is a measure of hydrogen ion (H+) concentration in water. It indicates the relative acidity or basicity of pool water. pH is measured on a scale of 0 (strong acid) to 14 (strong base) with 7 being the neutral pH.

In pools a slightly alkaline pH of 7.4 to 7.6 is most desirable because this range is most comfortable to the human eye (human tears have a pH of 7.4.) and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming.

More simply it tells us whether or not the pool water is safe to swim in – county code requires that the pool pH be in the range of 7.2 – 7.8.