ONE sample should be collected from a location within the distribution system that reflects maximum residence time of water in the system.


        THREE samples should be taken at representative locations within the distribution system taking into account the number of people, different sources, and different treatment methods. Systems may wish to collect representative samples at locations representing at least average residence time.


HAA5 and TTHMS should be collected from the same locations and preferably at the same time. If these are not collected at the same time, they should be collected during the same quarter. The location should stay the same for each of the four (4) quarters. Systems on reduced TTHM monitoring may continue to collect one sample per quarter per treatment plant from the point of maximum residence time.


If you have questions about sample collection points contact the Department of Health/Chris McMeen 206-389-2767.




1)      If water taps are to be used for sampling all aerators, strainers, and hose attachments need to be removed. Open the tap and allow the system to flush until the water temperature stabilizes. Adjust the flow to about the thickness of a pencil. When no air bubbles are visibly detected collect the sample from the flowing system. Fill the sample bottles to just overflowing but take care not to flush out the sample preservative. After collecting the sample seal the bottle and agitate by hand for 1 minute.

2)      Collect 1 250 ml bottle at each collection point for Method 552.1



IMPORTANT: Be careful not to touch or otherwise contaminate the inside lid or the lip of the bottle during sampling.


3)      All samples need to be kept cold. If the samples are to be held for a day prior to transporting to the lab, place the bottles in a refrigerator. Once samples are ready to be transported to the lab, add a bag of ice to the cooler. Samples must be received at Twiss Analytical Laboratories, Inc. within 48 hours of sampling.

4)      Insert the complete sample information (WSI) form into a plastic bag and place in the cooler. Please contact Twiss Analytical Labs at (360) 779-5141 if you have any questions.