Water Quality Analyses
Annual Analyses of Cedar and Tolt River water supplies
Federal and state regulatory agencies mandate the testing of numerous parameters in drinking water to ensure its safety.
These parameters are classified as:
- Primary Standards, which relate to public health. The public is notified if any of these parameters are exceeded.
- Secondary Standards, which relate to aesthetic qualities such as taste, odor and appearance.
- Unregulated parameters are monitored in the interest of our customers, or to assist regulators in developing future regulations.
Before you proceed, you'll want to know which source provides your drinking water.
2012 Quarterly Analyses
- 1st Quarter Analyses (pdf)
Archived Analyses
Is the Cedar River or the Tolt River the source of your water?
For Seattle Public Utilities' retail customers, the Cedar distribution system usually consists of areas south of the Lake Washington Ship Canal as well as lower elevations north of the Ship Canal.
Areas of higher elevation north of the Ship Canal usually receive water originating from the Tolt River.
Interpreting the tables
Here is some more information regarding individual columns in the water quality analysis tables:
- Column 1: Lists each category and parameter in drinking water for which we test. Information on most of these parameters is supplied in the EPA's Contaminant Specific Fact Sheets.
- Column 2: Lists the current or proposed maximum contaminant levels (MCLs) for each parameter if there is one, or the Residential Action Level in the case of lead and copper. To comply with state and federal standards, drinking water may not contain more than the MCL.
- Columns 3 & 4: List the levels of parameters observed in Seattle's sampling program for treated Cedar and Tolt water.
- Column 5 (for 2001 and later): List the minimum reporting level for each parameter. If a result is listed as ND (not detected), the result was below the minimum reporting level for that parameter.
Additional information
In the routine monitoring that Seattle Public Utilities is required to conduct, there are a large number of compounds that are not detected, because of the protected and pristine nature of Seattle's watersheds.
Seattle Public Utilities' Water Quality Annual Reports (Consumer Confidence Reports) provide additional information about drinking water sources, protection, treatment, testing, and compliance.
Related links
Water Quality Laboratory
Water Quality Planning and Engineering
Glossary of Drinking Water Terms