There is no central government database that allows officials to monitor water tests by local systems.

Some officials overseeing local water systems have tried to go above and beyond what is legally required. But they have encountered resistance, sometimes from the very residents they are trying to protect, who say that if their water is legal, it must be safe.

There are systems called zero discharge emission systems that would prevent any pollution from making it into the water or the air.

The Safe Drinking Water Act was passed in 1974 after tests discovered carcinogens, lead and dangerous bacteria flowing from faucets in New Orleans, Pittsburgh and Boston and elsewhere.

One goal of the Clean Water Act of 1972 was to upgrade the nation's sewer systems, many of them built more than a century ago, to handle growing populations and increasing runoff of rainwater and waste.

It is often difficult to definitively link a specific instance of disease to one particular cause, like water pollution. Even when tests show that drinking water is polluted, it can be hard to pinpoint the source of the contamination.