Homeowners who rely on a private well for their drinking water should have that water tested yearly for bacteria and contaminants, according to the Water Quality Association. Around 15 percent of the US population relies on wells or other individually owned sources of drinking water. US EPA’s Safe Water Drinking Act regulates public drinking water systems but not private sources, so it is up to the well’s owner to make sure its water is potable. The agency recommends yearly tests for total coliform bacteria, nitrates, total dissolved solids and pH levels. In addition, consumers should check with the local health department to see if there are other common local contaminants that should be checked. Some states may mandate testing for certain contaminants, according to the National Groundwater Association (NGWA).