An independent research group suggests sampling water in 720 West Virginia homes for a chemical that spilled into the water supply in January.
Researchers from the West Virginia Testing Assessment Project, or WV TAP, say that number of homes would be "statistically defensible" in determining whether affected households are chemical-free.
The group sampled 10 homes in February for crude MCHM using state taxpayer dollars. Each contained chemical traces, but the concentrations were about 675 times weaker than what federal officials call safe to drink. The report says levels of the chemical have continued to decline since the spill.