Seattle Public Utilities Ray Hoffman, Director

Water Quality Results

The results of monitoring in 2015 are shown in the tables below. These results are for parameters regulated by the federal and state agencies. For other water quality information, please see Water Quality or call (206) 615-0827. We can also send you a list of the more than 200 compounds for which we tested but did not find in our surface water supplies, including unregulated contaminants.

Water quality monitoring data can be difficult to interpret. To make all the information fit, we used many acronyms that are defined below the table. In Seattle, if you live south of Green Lake, your water probably comes from the Cedar. Areas north of Green Lake usually receive Tolt water. Each source can provide water to other areas in Seattle if needed.

Monitoring Results

 EPA’s Allowable LimitsLevels in Cedar Water
Detected CompoundsUnitsMCLGMCLAverageRangeTypical Sources
Raw Water
Total Organic CarbonppmNATT0.70.5 to 1.5Naturally present in the environment
Cryptosporidium*#/100LNANANDNDNaturally present in the environment
Finished Water
Turbidity (cloudiness)NTUNATT0.40.1 to 1.2Soil runoff
Arsenicppb0100.50.4 to 0.7Erosion of natural deposits
Bariumppb200020001.6one sampleErosion of natural deposits
Bromateppb010NDNDBy-product of drinking water disinfection
Chromiumppb1001000.270.25 to 0.33Erosion of natural deposits
Fluorideppm440.80.7 to 0.9Water additive that promotes strong teeth
Nitrateppm10100.01one sampleErosion of natural deposits
Seleniumppb5050NDNDErosion of natural deposits
Uraniumppb030NDNDErosion of natural deposits
Coliform, Total%05Highest Month = 0.4%
Annual Average = 0.035%
Naturally present in the environment
Total TrihalomethanesppbNA803826 to 43By-products of drinking water chlorination
Haloacetic Acids(5)ppbNA604118 to 41
ChlorineppmMRDLG=4MRDL=4Average = 0.88
Range = 0 to 1.7
Water additive used to control microbes
*Cryptosporidium was not detected in any samples from the Cedar (out of 3) and in one sample from the Tolt (out of 4).

 

 EPA’s Allowable LimitsLevels in Tolt Water
Detected CompoundsUnitsMCLGMCLAverageRangeTypical Sources
Raw Water
Total Organic CarbonppmNATT1.51.2 to 1.8Naturally present in the environment
Cryptosporidium*#/100LNANANDNDNaturally present in the environment
Finished Water
Turbidity (cloudiness)NTUNATT0.070.04 to 1.4Soil runoff
Bariumppb200020000.60.4 to 0.7Erosion of natural deposits
Arsenicppb0101.3one sampleErosion of natural deposits
Bromateppb0100.4ND – 2By-product of drinking water disinfection
Chromiumppb1001000.2ND - 0.24Erosion of natural deposits
Fluorideppm440.80.7 to 0.9Water additive that promotes strong teeth
Nitrateppm10100.10one sampleErosion of natural deposits
Seleniumppb5050NDNDErosion of natural deposits
Uraniumppb030NDNDErosion of natural deposits
Coliform, Total%05Highest Month = 0.4%
Annual Average = 0.035%
Naturally present in the environment
Total TrihalomethanesppbNA806226 to 91By-products of drinking water chlorination
Haloacetic Acids(5)ppbNA604826 to 68
ChlorineppmMRDLG=4MRDL=4Average = 0.88
Range = 0 to 1.7
Water additive used to control microbes
*Cryptosporidium was not detected in any samples from the Cedar (out of 3) and in one sample from the Tolt (out of 4).

Lead and Copper Monitoring Results

Parameter and UnitsMCLGAction Level+2013
Results++
Homes Exceeding Action LevelSource
Lead, ppb01530 of 50Corrosion of household plumbing systems
Copper, ppm1.31.30.100 of 50
+ The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.
++ 90th Percentile: i.e., 90 percent of the samples were less than the values shown.

Although there is no detectable lead in our source water, tests show there are sometimes elevated levels of lead and copper in some samples, primarily because of corrosion of household plumbing systems. These results show that it is very important that homeowners, business owners and others be aware of their type of plumbing, and how the plumbing affects their drinking water quality.

The majority of homes have some risk of lead contamination in water that sits in pipes for longer than two hours. Where you live, when your plumbing was installed and what type of plumbing you have, all play a part in determining your potential exposure level. SPU treats the water to minimize the tendency for lead to enter the water, and results show that that we have been very successful at this.

If present, elevated levels of lead can cause serious health problems, especially for pregnant women and young children. Lead in drinking water is primarily from materials and components associated with service lines and home plumbing. SPU is responsible for providing high quality drinking water, but cannot control the variety of materials used in plumbing components. When your water has been sitting for several hours, you can minimize the potential for lead exposure by flushing your tap for 30 seconds to 2 minutes before using water for drinking or cooking. If you are concerned about lead in your water, you may wish to have your water tested. Information on lead in drinking water, testing methods, and steps you can take to minimize exposure is available from the Safe Drinking Water Hotline or the at the EPA website.

Finally, remember that drinking water is only a minor contributor to overall exposure to lead. Other sources, including paint, soil, and food, also contribute.

Definitions

MCLG: Maximum Contaminant Level Goal—The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety.

MCL: Maximum Contaminant Level—The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology.

MRDL: Maximum Residual Disinfectant Level—The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

MRDLG: Maximum Residual Disinfectant Level Goal—The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.

TT: Treatment Technique—A required process intended to reduce the level of a contaminant in drinking water.

NTU: Nephelometric Turbidity Unit—Turbidity is a measure of how clear the water looks. The turbidity MCL that applied to the Cedar supply in 2013 was 5 NTU, and for the Tolt it was 0.3 NTU for at least 95 percent of the samples in a month. 100 percent of the samples from the Tolt in 2013 were below 0.3 NTU.

NA: Not Applicable

ND: Not Detected

ppm: 1 part per million = 1 mg/L = 1 milligram per liter

ppb: 1 part per billion = 1 ug/L = 1 microgram per liter

1 ppm =1000 ppb