Date: Sept. 15, 1999
Contacts: Bob Ludwig, Media Relations Associate
Jennifer Cavendish, Media Relations Assistant
(202) 334-2138; e-mail <>

New York City's Plan to Protect Drinking Water Should Focus
More on Controlling Dangerous Pathogens

WASHINGTON -- A comprehensive plan for safeguarding the supply of high-quality drinking water to New York City should place the greatest importance on preventing and controlling disease-carrying pathogens, says a new report from a committee of the National Research Council of the National Academies. Currently, the main target of the city's watershed management strategy is phosphorus, which can play a large role in degrading water quality but by itself is not toxic.

"Pathogens such as Cryptosporidium and Giardia pose a significant and direct threat to public health because they are very resistant to the chlorination process used to disinfect the city's unfiltered water supply," said committee chair Charles O'Melia, professor of geography and environmental engineering at Johns Hopkins University, Baltimore. "Efforts to monitor, model, and control these organisms must be stepped up."

The New York City Watershed Memorandum of Agreement was signed in 1997 after years of negotiations between city officials and representatives from the U.S. Environmental Protection Agency, state government, environmental groups, and municipalities around the watershed regions that supply the city with water. The National Research Council study was undertaken at the request of the New York City Comptroller's Office to provide a scientific evaluation of implementing the agreement.

The massive, multijurisdictional agreement calls for a complex amalgam of programs and policies for land acquisition and management, new health and environmental regulations, and financial assistance to communities that will limit growth to preserve the watersheds. It also will allow the city to avoid the need for filtering water from one of the two watersheds that supply the city until at least 2002 and should help maintain existing high-quality drinking water over the next several years, the report says.

Overall, the committee hailed the city's watershed management plan as a prototype for water suppliers nationwide. However, growing scientific understanding of the impacts of pollutants on human health, changing environmental regulations, and the uncertainties about the origin of specific pollutants demand that the city continually re-evaluate the need to employ filtration or other technologies to keep the water safe. Specifically, the report encourages water system managers to continue to consider treatment beyond chlorination to control dangerous pathogens, bacteria, and viruses. This dual approach -- implementing a watershed management plan, while investigating treatment processes that could be needed in the future -- will ensure that no time is lost if additional water treatment should become necessary.

The city's movement toward a comprehensive watershed plan can be traced to more stringent environmental regulations dating from 1989, which require suppliers to filter surface water in addition to disinfecting it, unless a watershed management plan is implemented. New York City gets its drinking water from two upstate watershed systems -- the Catskill/Delaware, which includes five counties west of the city in the Catskill Mountains and the headwaters of the Delaware River, and the Croton region north of the city. The water supplies serve an estimated 9 million people and produce up to 2 billion gallons of water each day.

The city already has committed to filtering the Croton system, which accounts for 10 percent of its water supply and is located in a more densely populated area. However, the ambitious watershed strategy for the unfiltered 90 percent from the Catskill/Delaware system is unprecedented because of its overall size and cost, and the implications for public and environmental policy, said the committee.

Pathogen and Chemical Control

Although a wide variety of microbes can cause waterborne illness, most bacteria and viruses can be controlled by disinfection. Pathogenic protozoa, however, are much more resistant to this process. The watershed management plan must incorporate a more rigorous strategy to study wildlife, domestic and farm animals, and human waste water to determine their contribution as a source of microbial pathogens, the report says. In addition, best management practices used to limit the amount of pollutants in reservoirs must be tested to determine their effectiveness in removing pathogens.

A Cryptosporidium risk analysis should be performed on a regular basis throughout the watershed, the report says. These periodic assessments can help determine the contribution of the city's watershed management strategy to overall reduction of risk from waterborne disease.

After pathogens, organic carbon compounds that lead to the formation of disinfection byproducts should receive priority attention, the report says. Many of these compounds are derived from natural sources and can be extremely difficult to control. Chlorine used in the disinfection process interacts with the organic matter and can form potentially toxic chemical compounds in drinking water. Organic compounds can be partially controlled by monitoring the level of phosphorus, which enters the water supply through a variety of means, including sewage treatment plants, agriculture, and urban storm-water runoff. Because phosphorus is a nutrient for algae and other plant growth in reservoirs, high concentrations of phosphorus can accelerate algal growth and increase the amount of organic matter in the water.

Storm-Water Runoff

Nature has a great capacity to remove pollutants from storm water. However, this capacity is compromised in agricultural and urban areas, resulting in an increased delivery of pollutants to streams and rivers via storm water. The watershed agreement includes programs such as a storm-water pollution prevention effort and a plan focusing on agricultural runoff, all designed to protect the water supply from "non-point" sources of pollution. But they have proven only partially successful in removing pollutants from runoff, the committee said, and most have not been tested for their ability to control pathogens.

For example, one of the most prevalent features of the watershed agreement is the use of "setbacks" to protect wetlands, streams, and reservoirs from pollution by prohibiting activities within certain distances of a body of water. While the widths of setbacks are defined in the watershed plan, the committee noted that the agreement does not discuss characteristics of the land, such as slope, soil moisture, or vegetation, which all play a role in removing pollutants. Monitoring of these areas is greatly needed to determine whether the proscribed setback distances are adequate.

Waste-Water Treatment

The watershed agreement requires that waste-water treatment plants be upgraded, using the best available technology to control dangerous chemicals and microbes. These improvements should be effective in reducing threats to the water supply, the report says, because a major factor in determining the quality of New York City drinking water is the treatment and disposal of wastewater in the Catskill/Delaware watershed. Nearly all of the waste water from the region is either discharged directly into tributaries that lead to the reservoirs or seeps below ground, where it eventually reaches the reservoirs.

However, similar technology upgrades have not been required for septic systems, which serve individual residences. For failing and new septic systems, New York City should install aerobic treatment units, which use mechanical devices such as pumps to create better oxygen flow within septic tanks. Without such action, pollutants in the water supply are expected to increase along with population growth. This recommendation is especially important in the Kensico watershed, which is experiencing substantial population growth and which is served almost entirely by septic systems.

Balanced Strategy

The agreement's overall framework for balancing the need for environmental rules and regulations to protect the watershed and supporting limited development in watershed communities is a sound strategy for the city, the report says. New York City plans to spend about $1 billion over the next 10 years to implement its watershed plan and part of the money is earmarked to help communities that may suffer economically because they must limit the amount of development they undertake.

While even limited population growth and increased economic activity in the watershed region will have some adverse impacts on water quality, the report says that the combination of better planning, targeted development, tougher environmental regulations, and improved waste-water management will ensure existing high water quality. Further, the committee examined existing data that track trends in population growth and found that growth in the Catskill/Delaware watershed is not accelerating.

To preserve environmentally sensitive areas in the watershed, the city also has budgeted $250 million over the next 10 years to purchase 355,000 acres of land held by private owners. In tandem with this effort, government officials should frequently employ land-use computer models to better determine specific parcels of land that are contributing to water quality problems, the report said.

The study was funded by the New York City Comptroller's Office. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.

Read the full text of Watershed Management for Potable Water Supply: Assessing New York City's Approach for free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web site or at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information at the letterhead address (contacts listed above).

A statement by committee chair Charles O'Melia is also available.

Commission on Geosciences, Environment, and Resources
Water Science and Technology Board

Committee on Watershed Management for New York City

Charles R. O'Melia* (chair)
Professor of Geography and Environmental Engineering
Johns Hopkins University

Max J. Pfeffer (vice chair)
Associate Professor
Department of Rural Sociology
Cornell University
Ithaca, N.Y.

Paul K. Barten
Lecturer in Hydrology and Watershed Management
Yale University
New Haven, Conn., and
Associate Professor of Forest Resources Management
University of Massachusetts

G. Edward Dickey
Consultant, and
Adjunct Professor of Economics
Loyola College in Maryland

Margot W. Garcia
Associate Professor
Department of Urban Studies and Planning
Virginia Commonwealth University

Charles N. Haas
Betz Chair Professor of Environmental Engineering
Drexel University

Richard G. Hunter
Deputy State Health Officer
Florida Department of Health

R. Richard Lowrance
Agricultural Research Service
U.S. Department of Agriculture
Tifton, Ga.

Christine L. Moe
Department of Epidemiology
University of North Carolina
Chapel Hill, and
Adjunct Professor
Division of Environmental and Occupational Health
Emory University School of Public Health

Cynthia L. Paulson
Environmental Engineer
Brown and Caldwell Associates

Rutherford H. Platt
Professor of Geography and Planning Law
Department of Geosciences
University of Massachusetts

Jerald L. Schnoor*
University of Iowa Foundation Distinguished Professor of Environmental Engineering, and
Center for Global and Regional Environmental Research
University of Iowa
Iowa City

Thomas R. Schueler*
Executive Director
Center for Watershed Protection
Ellicott City, Md.

James M. Symons*
Cullen Distinguished Professor Emeritus of Civil Engineering
University of Houston
Bradenton, Fla.

Robert G. Wetzel
Bishop Professor
Department of Biological Sciences
University of Alabama


Laura Ehlers
Study Director

* Member, National Academy of Engineering