The Suffolk County Department of Health Services is seeking public comment, due by March 1, on a new plan to manage, conserve and protect the county's water supply, whose quality continues to slip.

Nitrogen was among the worrisome trends: the nutrient leaches into groundwater from septic systems and fertilizer use. Seventy-five percent of county households use septic systems, according to Newsday.

While 98 percent of raw water tested met health standards, nitrogen levels have increased by about 1 milligram per liter over the past two decades, the report found.

Excessive nitrogen can cause health problems in infants. Nitrogen-laden groundwater also seeps into streams and bays, triggering algae blooms that suck oxygen from the water and harm marine life.

Pesticides and industrial chemicals - many of them ingredients in common household products - continue to turn up in groundwater. Some, like the dry-cleaning solvent tetrachloroethylene, have as much as doubled between 1987 and 2005 in the same set of drinking water wells tested, the report found. Trace levels of prescription drugs and personal care products, like shampoo, also turned up in supply wells and private wells. Little is known about their cumulative health impact.

The plan also forecast rising demand. It highlighted summer spikes in water use for landscaping -particularly automatic systems that go on even when it's raining - that could require costly new infrastructure. Future development on the East End of Long Island likely will require dozens of new wells, and the report advised conservation measures - such as seasonal rate hikes - to prevent further stresses on the system.