Bacterial contamination is very common.
Studies show that more than 40 percent of private water supplies are contaminated with coliform bacteria. Spring-water supplies are the most frequently contaminated, with more than 70 percent containing coliform bacteria. Next, consider improving protection of a well or spring from the inflow of surface water if the supply is contaminated with bacteria. Although well pits were the common method of construction several years ago, they are no longer considered sanitary construction. The well casing of a properly protected well extends above the surface of the ground.