Clean up that dirty water

FOR DECADES, the state and federal governments have acted in tandem to end the high levels of bacterial contamination in the state's rivers, with the goal of making once heavily polluted waters swimmable and fishable. Full restoration of rivers to good health remains elusive, however, because of another pollutant: phosphorus.

This all-too-pervasive nutrient promotes the growth of algae that kill fish life and are often toxic to humans, so environmental regulators are now going after it - starting with the Charles River. Such action is long overdue.

For the first time in the United States, the US Environmental Protection Agency will require changes in the operations of the shopping malls, manufacturing plants, and big housing complexes whose parking lots and roofs are the major sources for much of the phosphorus. Storm water carries the phosphorus, much of it generated by auto exhaust and dead leaves, into the region's rivers.

The EPA is focusing its cleanup enforcement on a pilot project involving three upstream towns of the Charles River watershed: Milford, Bellingham, and Franklin.

Owners of large paved areas will be able to reduce their runoff with a range of measures, including the installation of porous pavements, the reconfiguring of parking lot landscaping into below-grade islands, and the creation of nearby artificial wetlands or ponds. Two nonprofit activist organizations, the Charles River Watershed Association and the Conservation Law Foundation, have pushed for EPA action.

Meanwhile, the Massachusetts Department of Environmental Protection this week is unveiling its own statewide storm water management program. It, too, will require the most extensive modifications from property owners in the Charles River watershed. Elsewhere, the department says, property owners will be "required to implement good housekeeping measures, such as regular parking lot sweeping." Storm water, says DEP commissioner Laurie Burt, "is the new frontier of clean water."

Regulators are focusing their attention on private-sector sources of pollution in part because municipalities have already made major investments in storm drainage and waste water treatment.

Directing storm water runoff from paved areas into the ground and away from rivers serves two purposes. In addition to preventing the kind of algae buildup that forced the cancellation of the Charles River swimming race in 2006, it also helps recharge groundwater sources. These supply much of the region's drinking water and keep its streams from drying up.

Rain water is a terrible thing to waste - or to become a vehicle for the pollution of the nation's rivers.