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Public Health - Seattle & King County

How to take bacteriological samples from your small water system

A bacteriological test is required once each year and a nitrate test once every three years.

There are several options you can choose from to fulfill this requirement, but perhaps the quickest and most economical is to take the sample yourself. For a bacteriological test you can visit either of our Environmental Health Services offices listed below, pick up a sample water bottle, take the sample according to the directions provided, and return it. In approximately two weeks you will receive a report of the lab's findings.

While we do not perform nitrate tests, the Washington State Department of Ecology can assist you with questions about nitrate testing at 425-649-7000 or you may visit their website at www.ecy.wa.gov/programs/eap/labs/search.html which includes a list of labs that can do water testing for private wells.

If you prefer, you can also contact a private laboratory and request that they perform your water tests. Check your phone directory's yellow pages under "Laboratories" or visit the Yellow Pages online; make sure that the lab you choose is state-certified for bacteriological and nitrate testing. Or, contact us and we will send you a list of certified private labs.

The following is Public Health's procedure for taking your own bacteriological sample: (This procedure applies only when the Seattle-King County Health Department Lab is performing the bacteriological analysis.)

  1. Obtain a bacteriological water bottle from one of the Environmental Health Services offices listed below.
  2. Find the farthest possible water tap from your water source. If the tap has a screen on it, remove the screen. Start the water and let it run for three to four minutes to clear the pipes.
  3. Open the water bottle. Do not touch the inside of the bottle or cap, and do not rinse out the bottle (the granules or drop of liquid inside the bottle are there to stabilize the bacteria population of the sample).
  4. Fill the bottle with water up to the line near the top. If there is no line on the bottle, fill it only to the break of the shoulder. Be sure to use cold water.
  5. Put the lid firmly back on the bottle.
  6. Complete the "Water Bacteriological Analysis" form that came with the bottle. Be sure not to write in the shaded sections (except where it asks for I.D. No.) or below the red line. If you do not have the six-digit I.D. number, call the Eastgate district office, (206-296-4932) to determine your number.
  7. Return the bottle and all copies of the "Water Bacteriological Analysis" form to the health department as soon as possible, but no later than the following morning. If you have to wait until the next morning to return the sample, be sure to refrigerate the bottle overnight. (The sample must reach the lab within 30 hours of collection.)

You should be receiving a report with the water analysis findings within two to three weeks.

Water sample bottles are available at the following locations (click links below for current office hours):

Contact us

Environmental Health Services
Administrative Offices

401 5th Ave., Ste. 1100
Seattle, WA 98104

Phone: 206-263-9566

Eastgate Environmental Health
14350 SE Eastgate Way
Bellevue, WA 98007

Phone: 206-296-4932

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