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Taking bacteriological samples from your small water system

Taking 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 to do a search for labs.

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.

The following is Public Health's procedure for taking your own bacteriological sample: (This procedure applies only when the Public Health Laboratory 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, (206-477-8050) to determine your number.
  7. Return the bottle and all copies of the "Water Bacteriological Analysis" form to Public Health 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.) Please do not return water samples to the Environmental Health Services Administration Offices at 401 5th Ave, Suite #1100 in Seattle, as they cannot be processed for testing at this location.

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:

What to do when a private well receives an unsatisfactory bacteriologic test result

When a lab report on the well water sample you submitted shows that it has exceeded the allowable bacterial standards for drinking water, please follow the procedures outlined below to try to eliminate the source of contamination.

For drilled wells:

  • Examine the equipment for breaks, leaks, rust, and disrepair. Verify that the top of the drilled well has a sanitary seal (a rubber gasket held in place by bolts through the top of the well). The bolts, as they are tightened, compresses this rubber gasket to form a tight seal to the sides of the casing. Check where the electrical wires go through the top of the well casing, and see if there are any gaps between the wires and the casing openings. The area around the wires should be sealed with putty, silicone caulk, or other suitable material. This prevents the entrance of insects, small animals, and dirt into the casing. The well casing vent (usually shaped like a candy cane) should be covered at the end of the vent with a fine mesh screen which also prevents the entrance of insects.
  • Examine the reservoir for algae, mold, slugs, and small animals. You may want to drain the reservoir and scrub the inside with a solution of 1 tablespoon household bleach in 1 gallon of water.
  • CAUTION: Make sure the area is well ventilated and do not use ammonia at all. Afterwards, make sure the lid is sealed with a gasket and that the overflow pipe is screened to prevent insects, rodents, etc. from getting into the reservoir. You should have a closed system, which means that there is no opening, no matter how small, between the water from the well and the faucets (except for properly screened vent and overflow pipe).
  • Disinfect the system. Please follow the instructions provided in the fact sheet "Disinfection of Private Wells." Follow the steps outlined for drilled wells.
  • Approximately 5 days after disinfection, you can take another water sample. Take it from a faucet as far away from the well as possible. If this sample is unsatisfactory, you may contact the public health department for advice or call a licensed well driller or water system designer.

For dug wells:

  • Dug wells, because they are shallow and the water is not from a protected aquifer, are usually easily contaminated and not easily decontaminated. Please follow the instructions provided in the fact sheet "Disinfection of Private Wells." Follow the steps outlined for drilled wells.
  • You need to make sure that the source is as protected as possible. The inside of the well should be lined with concrete tile or other durable material, and a protective cover should be placed over it. The cover should have a built-up edge under it, to prevent water and dirt from running into the well. It should a have a gasket to seal the opening. Concrete (with handles) is the preferred material for the cover.
  • The area around the well should be free from sources of contamination (such as a drainfield, septic tank, pasture, barn, garage) for 200 feet in any direction.
  • If your efforts at decontamination have no effect, you should consider connecting to another, approved source of water, drilling a new well, or adding a chlorinator.

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