BOX 2-4
The Presence of Wastewater in Drinking Water Supplies Circa 1980

A survey of wastewater discharges upstream of drinking water intakes was conducted on behalf of EPA, reflecting water systems that collectively served 76 million persons (Swayne, et al., 1980). Data are shown in the below figure for average flow conditions and low flow (i.e., 7-day, 10-year low flow) conditions. Utilities serving 32 million people (of the 76 million total reflected in the survey) reported that no wastewater was discharged upstream of the water intakes. However, of the remaining 44 million people served by the utilities surveyed, more than 20 million relied upon source water with a wastewater content of 1 percent or more under average flow conditions, and a similar number relied on source water with a wastewater content of 10 percent or more during low-flow conditions. No comparable more recent data are available, but these percentages have likely increased significantly since the EPA data were collected, given the population growth and increasing water use over the last 30 years. Although some of the supplies represented by the data on the right side of the figure below are controversial, most of these urban water supplies are considered safe, conventional water supplies by the public.

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Persons served by a water supply with wastewater content according to EPA’s 1980 survey of wastewater discharged upstream of drinking water intakes.
SOURCE: Data from Swayne et al. (1980).

the United States through the EPA’s Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) system3 and have been adapted by scientists working for the pharmaceutical industry to make such calculations for 11 watersheds serving as drinking water supplies for 14 percent of the U.S. population (Anderson et al., 2004). Maps that show the contribution of wastewater under current and future scenarios could be extremely useful to water resource planners and public health experts as part of efforts to manage the nation’s water resources in a safe and reliable manner.

USGS maintains stream gauging stations and has an active research and monitoring program for wastewater-derived contaminants. EPA has considerable experience in the development and application of surface water quality models. Through a collaborative effort drawing upon the expertise of both agencies, agency scientists could provide water resource planners with a better understanding of the extent of de facto reuse in their catchment and provide data useful to estimating contaminant attenuation between effluent discharge and potable water intakes (e.g., residence time, water quality, depth).

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3 See http://water.epa.gov/scitech/datait/models/basins/index.cfm.



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