Legend: This map highlights regional patterns of dependence on intermittent, ephemeral, and headwater streams for surface drinking water by
county. Across the nation, 357,403 total miles of streams provide water for surface water intakes supplying public drinking water systems; of this,
207,476 miles, or 58%, are intermittent, ephemeral, or headwater streams. Nationwide, over 117 million people receive drinking water from public
drinking water systems that rely at least in part on intermittent, ephemeral, or headwater streams. This analysis compared the stream length of
intermittent, ephemeral, and headwater streams to total stream length within all mapped Source Protection Areas (SPAs) for each county. A SPA is an
area upstream from a drinking water source or intake that contributes surface water flow to the drinking water intake during a 24-hour period. This is
based on data that generally do not include streams less than one mile in length. Intermittent streams are streams containing water for only part of
the year. Ephemeral streams flow only in response to precipitation events. First-order streams have been used to represent headwater streams.
Data Sources: National Hydrography Dataset Plus at medium resolution; Federal Safe Drinking Water Information System 4th Quarter 2006 Data.
Key:
Intermittent, ephemeral, and
headwater stream miles as
percentage of total stream
miles contained in all SPAs
for a given county
] o%
|] 1 % - 44%
H 45% - 56%
H 57% - 69%
| 70% - 86%
| 87% - 100%
|] No Data
Percentage of Surface Drinking Water from
Intermittent, Ephemeral, and Headwater Streams

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