Quality of Groundwater
For a region as a whole, the chemical and biological character of groundwater is acceptable for most non-potable uses. The quality of groundwater in some regions, particularly shallow groundwater, may be changing as a result of human activities. Groundwater is less susceptible to bacterial pollution than surface water because the soil and rocks through which groundwater flows screen out most of the bacteria. Bacteria, however, occasionally find their way into groundwater, sometimes in dangerously high concentrations. But freedom from bacterial pollution alone does not mean that the water is fit to drink. Many unseen dissolved mineral and organic constituents are present in groundwater in various concentrations. Most are harmless or even beneficial; though occurring infrequently, others are harmful, and a few may be highly toxic.