Enter in your zip code and you can check EWG's Tap Water Database for contaminants detected above health guidelines and other detected contaminants.  Good reasons to opt for water filters.

Since 2010, water utilities' testing has found pollutants in Americans' tap water, according to an EWG drinking water quality analysis of 30 million state water records.

https://www.ewg.org/tapwater

What you find might suprise you.  I put in a zip code for an area that is known for "good water" and there were 7 contaminants detected above health guidelines, and 8 other detected contaminants:

Includes chemicals detected in 2015 for which annual utility averages exceeded an EWG-selected health guideline established by a federal or state public health authority; chemicals detected under the EPA's Unregulated Contaminant Monitoring Rule (UCMR 3) program in 2013 to 2015, for which annual utility averages exceeded a health guideline established by a federal or state public health authority.

• Bromodichloromethane

  cancer✕

  ---

• Chloroform

  cancer✕

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• Chromium (hexavalent)

  cancer✕

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• Dichloroacetic acid

  cancer✕

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• Total trihalomethanes (TTHMs)

  cancer✕

  ---

• Trichloroacetic acid

  cancer✕

  ---

• Radiological contaminants

  • cancer