Millions of residents in the Big Apple enjoy unfiltered potable water, partly due to Cornell Cooperative Extension in Delaware County (CCE-DC) and its partners. Since 1992 they have been working to keep New York City's drinking water clean.

The city's water comes from the 1,580-square-mile Catskill/Delaware reservoir system west of the Hudson River and the 375-square-mile Croton reservoir system east of the river. Delivering more than 1.3 billion gallons of fresh water daily through a 6,000-mile grid of water mains, this is considered to be one of the largest, and cleanest, surface water collection systems in the world. But, with nearly 500 dairy and livestock farms located throughout these watersheds, farm runoff -- a major contributor of disease-causing protozoa and phosphorus -- has the potential to degrade water quality.

To combat these problems, the nonprofit Watershed Agricultural Council (WAC) partnered with CCE, the U.S. Department of Agriculture Natural Resources Conservation Service, and soil and water conservation districts to develop "whole-farm" plans to help farmers reduce harmful farm runoff and protect the watershed.

Without a filtering process, New York City's water is potentially vulnerable to such parasitic protozoa as Giardia lamblia, and cryptosporidium from manure, which can cause intestinal disease and diarrhea in humans. In addition, phosphorus from manure and fertilizers increase algae, which, when combined with chlorine treatment, can create chemical byproducts that can have long-term toxic impacts for humans.

To identify sources of these waterborne pathogens in the Cannonsville watershed, Hussni Mohammed, an epidemiologist at Cornell's College of Veterinary Medicine, is working to understand how they are introduced to the system and determine what factors are contributing to their survival. His work is used to inform farmers about the risks associated with these and similar pathogens and how they can manage livestock to reduce disease.

Expensive filtration measures are not needed, thanks to farm conservation practices, upgrades to sewage treatment systems and other projects that aim to keep the water clean.

This so-called whole-farm planning includes diagnosing the pollution sources, putting conservation practices in place and tracking farm systems through regular visits from a watershed planning team. CCE and Cornell have helped create nutrient- management plans for every farm participating in the watershed program. Conservation practices can include guidance on the amount and placement of animal manure and fertilizer, fencing cows out of streams, directing clean water away from farmsteads and establishing vegetative buffer zones to filter barnyard runoff and milkhouse waste.

Research by the New York State Department of Environmental Conservation has shown that farm phosphorus runoff can be reduced by 30 percent through an effective whole-farm plan.

"Watershed farmers work hard to implement and maintain best management practices, and the city has been true to their commitment to pay the cost to plan, design and construct them. It has been a true win-win," said John Thurgood, watershed agricultural extension program leader for CCE-DC.

A major issue is how to reduce phosphorus imported from outside the farm in the form of cattle feed. Most of this phosphorus comes out in the cattle manure that is then applied to farmland, which increases the amount of nutrients in New York City's watershed ecosystem.

"Before they imported feed from outside, the system was in equilibrium," said Tammo Steenhuis, a Cornell professor of biological and environmental engineering who has been researching cost-efficient ways to reduce dissolved phosphorus in the watershed. The strategy, he said, is to monitor phosphorus and water movement and place manure furthest from streams where runoff is generated.

Animal science professor Larry Chase added that farmers often feed their livestock more nutrients than they need for optimal health. "Our earlier work indicates that if no best-management practices are implemented, then phosphorus levels are going to increase, because there is more phosphorus going into the watershed than is leaving it," said Christine Shoemaker, a Cornell professor of civil and environmental engineering. Shoemaker and her students have developed a computer model that takes into account land uses and soil types and tracks the movement of water, sediment and phosphorus in the 47-square-mile Cannonsville watershed.