Water quality in Suffolk is on an "alarming" downhill slide, and a sweeping county report being prepared on how to manage the drinking water supply offers few concrete solutions to halt the decline, environmental advocates said Monday.

While public water remains safe and is routinely tested for a range of contaminants, the source of the supply -- groundwater pumped from underground aquifers -- is increasingly fouled by nitrogen and other pollutants, according to a draft water management plan that Suffolk health officials released late last year.

"At this rate, by 2050 we're in a serious problem here," Adrienne Esposito, executive director of Citizens Campaign for the Environment, said at a news conference Monday overlooking the Carmans River in Yaphank. "The systematic development of the land surface is causing the degredation of the water supply."

Suffolk officials defended the report, which should be finalized late this year or early next year. They said efforts were already under way to protect local groundwater, including studies on whether to install sewers in more than 20 areas around the county. About three-quarters of Suffolk relies on cesspools and septic systems, which discharge nitrogen to groundwater.

The county report recommended more groundwater monitoring, and said the county should put a priority on open space preservation near drinking water wells and limit housing density in ecologically sensitive areas without sewers. Public comment on the draft ended earlier this month.

"The plan does a very good job to keep the public drinking water supply safe," said Walter Dawydiak, chief engineer for the health department.

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But Esposito and other conservation advocates said regulators must take bolder steps to limit pollution from septic systems, pesticides and fertilizer use before it's too late.

Among the changes they'd like to see: scaled-back agricultural use of pesticides and fertilizer, and revisions to the Suffolk sanitary code to address pollution from aging cesspools.

Advocates also called for hearings on the decline in water quality. They said more must be done to protect sensitive bays and estuaries from nitrogen, which can wreak havoc in local ecosystems even at levels permitted by state drinking water standards.

Dawydiak said Suffolk was in the midst of evaluating advanced septic technologies that could reduce nitrogen pollution by up to 80 percent. "We're going to run scenarios, like how much would it cost to put them in areas of the Peconic Bay estuary."