Percentage of Surface Drinking Water from Intermittent,
Ephemeral, and Headwater Streams in Washington
Intermittent, ephemeral,
and headwater stream
miles as percentage of
total stream miles
contained in all SPAs
for a given county
2% - 44%
]] 45% - 56%
[] 57% - 69%
| 70% - !
| 86% - 100%
No Data
Legend: This map highlights regional patterns of dependence on intermittent, ephemeral, and headwater streams for surface drinking water in Washington. In Washington, 11,439 total
miles of streams provide water for surface water intakes supplying public drinking water systems; of this, 6,355 miles, or 56%, are intermittent, ephemeral, or headwater streams. Over 2
million people in Washington 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 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 4thQuarter 2006 Data.