The United States Environmental Protection Agency requires public water companies, utilities, etc. to monitor and report specific water quality parameters on a regular basis. You can find the full list of those parameters here.

“National Primary Drinking Water Regulations (NPDWRs or primary standards) are legally enforceable standards that apply to public water systems. Primary standards protect public health by limiting the levels of contaminants in drinking water.” (source)

The government regulates the introduction of and requires the removal of items listed in the Primary Drinking Water Standards if they exceed Maximum Contaminant Levels (MCL’s) because scientists and health officials have concluded that overexposure to those items ingested via drinking water causes signifigant health risks in humans.

As always, when evaluating your drinking water for safety reasons, keep in mind that home water test kits work quite well as a screening tool in the field and that no one should rely colely upon the results of ANY field screening method when making the final determination as to whether or not they have safe drinking water.