The municipal water system of New York City has been one of the great assets of the metropolitan region for more than 150 years. Following a sequence of water-related crises in the first third of the nineteenth century, including cholera epidemics and fires (e.g., 1832 and 1835, respectively), major investments for physical infrastructure were made to collect and transport surface water from low population density areas north of the city. The quality and stability of NYC municipal supply made a major advance with arrival of water from the first Croton Reservoir in Westchester County during the summer of 1842. Dramatic expansion of watershed area, storage reservoirs, and aqueducts continued over the next century, resulting in the elaborate network which currently supplies NYC with water of generally high quality.
Four distinct components of the NYC water supply discussed here (all derived from surface waters) include Delaware, Catskill, Croton, and Hudson (used only during drought emergencies). Each of these has features that significantly affect current management practices and water quality. Of the total base supply (derived from an area of about 5.1 x 103 km2), upper Delaware River tributaries provide almost half of the watershed area (47 percent). This network, in the western Catskill region, was the most recently constructed and has generally high raw water quality. However, the West Branch, East Branch, and Neversink are tributaries of the Delaware River (Table 7.4) resulting in releases from NYC storage reservoirs being subject to regulations by an independent commission which must balance other municipal supply (primarily Philadelphia) and environmental needs with those of NYC. During an extended drought, when NYC has greatest need for diversion of water from Delaware tributaries, withdrawal limitations from storage due to competition with other demands in the Delaware basin are likely to be the most stringent. The Catskill drainage, with 34 percent of total watershed area, has similar raw water quality advantages as the upper Delaware basin for NYC, and is primarily dedicated to NYC demands. Its most significant limitation is size. There is not sufficient area to provide all of NYC water demand. The Croton System (19 percent of total watershed area), closest to consumers and earliest in construction, has lower raw water quality than the two components derived from the Catskill area. Situated in a region immediately north of NYC, pollutants associated with relatively high population density and extensive transportation corridors, the Croton watershed presents a more difficult challenge for NYC in terms of water quality management. The Hudson River is used as a source of water during drought emergencies, when water is pumped into the aqueduct system near Chelsea, following addition of chlorine and alum. Quality of Hudson River water, as reflected by a long history of persistent toxic influxes (Bopp et al., 1982;Bopp and Simpson, 1989), is appreciably lower than for most NYC watershed runoff. This situation presents a clear conflict between maintaining total supply quantity and quality during drought emergencies, resulting from blending of Hudson River water with the two major delivery flows derived from the Catskill Mountains.
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