After the Clean Water Act was passed, in 1972, America made significant progress in cleaning up its waterways. But in recent years, enforcement has slackened. Also, types of pollutants not covered by the act are more prevalent, compromising water quality in new ways. So it came as a welcome development when, at a hearing last month before the House Committee on Transportation and Infrastructure, the new administrator of the Environmental Protection Agency, Lisa P. Jackson, pledged a renewed commitment to water quality.

A recent New York Times series found a steady increase in violations of the Clean Water Act, with hundreds of thousands of breaches occurring in the last five years alone. Yet only a minuscule number of polluters has been punished. As examples, the series cited water contaminated by mining waste that has ruined teeth and caused painful rashes in West Virginia. Liquefied manure has seeped into Wisconsin wells, and pesticides are coming through the tap in other farm states. High concentrations of dry-cleaning solvent have turned up in drinking water in parts of the Northeast.

The Clean Water Act mainly addresses pollution from single sites, such as factories, garbage dumps and wastewater treatment plants. But “non-point” sources, such as runoff from lawns or farms, are also big polluters. One challenge for the EPA is to better track and curb pollution from these sources. It may need help from Congress, in the form of a revised law. (Other parts of the law, such as those pertaining to power-plant pollution, may need updating as well.)

While the number of potential polluters has grown, state enforcement budgets have not expanded significantly, and manpower has not kept pace. In addition, political pressure has kept many states fearful of cracking down. That must change. The EPA can help by signaling that it will not tolerate any tendency to look the other way. The agency has the authority to intervene when the states fail in their enforcement role. By doing so, it can send an important message.

It can be difficult to trace specific illnesses to toxins in drinking water. Chemicals may build up in the body over time. But they have been linked to a host of serious ills, including cancer, birth defects, fertility problems, organ failure, developmental problems and neurological diseases. Unfortunately, chemical pollutants are harder to see than the raw sewage that once flowed so openly into rivers and streams. Yet some of the illnesses now cropping up may be due to years of complacency. Public pressure can help ensure that the EPA and the states do their job, and that Americans can rely on their water.