A number of contaminants, including arsenic and nitrates, are hidden to the naked eye. In many cases, a single drinking water system will contain more than one hazardous chemical, making it difficult for individuals to evaluate the overall health risk.
"We're never exposed to just one agent," said Jamie DeWitt, an associate toxicology professor at East Carolina University.
DeWitt said even a reverse osmosis system — the one recommended by Erin Brockovich — can trap contaminated water in its filters. Though she uses a filtration system in her own home, she said it's mostly to remove the bad taste of chlorination byproducts.
Her main advice is to know your water source and read water quality reports from your local utility — even before you smell, taste, or see something bad.