There are State standards for over a 100 potential chemical and bacteriologic contaminants of drinking water. For example, the maximum allowable level for nitrates in drinking water is 10 milligrams per liter. This link provides a listing of these maximum allowable levels. One California study has indicated that there might be a relationship between miscarriage rates and tap water containing a group of chemicals called TTHMs. This article discusses that study.
Some water systems maintain their own web pages, which can be of value to their customers.
Go to this link to see if your water system is listed. In an emergency . . .