Acid Water. Secondary MCL: pH between 6.5 and 8.5
A water supply may be too acidic because of acid rain, contamination from acid mine drainage, or it may simply be “too pure” (like distilled) and have insufficient alkalinity to buffer the water against atmospheric acids. The secondary MCL becomes mandatory in the U.S. only if it is necessary to control the corrosion of lead- and copper-containing plumbing materials. (Other materials also corrode, but they are less toxic.)
The remedy is to add alkalinity to the water, and there are two approaches. If it is a private well that is being or is to be chlorinated, it is a simple matter to add a solution of sodium carbonate (“soda ash”, Na2CO3), or sodium hydroxide (“caustic soda”, NaOH), to the chlorine bleach. If there is no chemical pump, use granular bed filters containing calcite (calcium carbonate: ground limestone or marble) or magnesia (magnesium oxide) media, or a mixture of the two. These dissolve slowly in the acid water, consuming excess acid and providing the water with additional hardness and alkalinity.