Total coliforms are found naturally in soil, surface water, plant material, and insects; however, one species of total coliform (E. coli) is found in the feces of warm blooded animals. Total coliforms are not naturally found in well water or groundwater. Wells should be tested yearly if there is a history of total-coliform-absent (bacteriologically safe) results, or more frequently if there is a change in the water quality because of color, taste or odor.