You read about the 300,000 West Virginians who don't know if they are drinking safe water — and ask "Could it happen here?" The answer is "You betcha!" Environmental journalists have many tools for discovering drinking-water disasters-waiting-to-happen in their own bailiwicks.
The contaminant MCHM was not on many people's radar; it was not on most EPA lists of chemicals to worry about. How about starting with chemicals that ARE on one of the lists? Read on.
SDWA UNREGULATED CONTAMINANTS. The Safe Drinking Water Act requires EPA to develop lists of contaminants which would be of concern if they got into drinking water — but which are not actually regulated by EPA. The larger public drinking water systems are actually required to test for these contaminants under the "Unregulated Contaminants Monitoring Rule (UCMR)."
SDWA requires utilities and EPA to disclose test results on unregulated contaminants to the public. More information here. 
SOURCE WATER ASSESSMENTS. The Safe Drinking Water Act also requires states to produce "Source Water Assessment" reports about the water going into public drinking water systems. The law requires states to inventory potential sources of contamination and to determine the susceptibility of the water supply to contamination.
This information is summarized for the public in "consumer confidence reports" and must be made available to the public. More information here. 
CONSUMER CONFIDENCE REPORTS AND NOTICES OF VIOLATION. Public drinking water systems must annually send their customers a "Consumer Confidence Report" on the quality of their delivered drinking water. Utilities are required to notify customers promptly if the delivered water violates EPA health standards because of contamination. Information about violations should also be in the CCRs. Many utilities put this information online.
Not every source water assessment is done well. In retrospect, the Freedom Industries chemical tanks a mile upstream of the Charleston drinking water intake might have seemed an obvious threat. The obscurity of the chemical MCHM probably made it harder to see. But there are hundreds of chemicals known to EPA to be health threats. See EPA's "List of Lists". 
SAFE DRINKING WATER INFORMATION SYSTEM (and widget). You may already have a problem in your area. EPA's Safe Drinking Water Information System (SDWIS) is a public, searchable, online database that allows you to find out about drinking water violations in your city, state, or ZIP code. It is even available as a widget you can use from your smart phone. More here. 
TOXICS RELEASE INVENTORY. If you want to know where there are large amounts of toxic or otherwise dangerous chemicals in your vicinity, start with the Toxics Release Inventory (TRI). This is an updated, searchable, online database that is publicly available. It only shows larger amounts of the most dangerous chemicals, but it is a great starting point. More information here.