Sampling and Sampling Stations: Who, What, Why, Where and How
Who is required to take samples?
All entities that are part of the water distribution chain, up to but not including the retail customer are required to sample and test the water flowing in their systems.
Who requires the samples?
The Feds, in the form of the ERA and each State Government (usually the state's DEP).
What are the requirements?
They are based on two factors: Customers served and recent experience. The range is from one sample per month for small systems, to hundreds of samples per month for larger systems. However, sampling requirements escalate if recent experience detects unacceptable levels of any of the tested-for contaminates.
Why is sampling performed?
The reason for the sampling is to detect and prevent contamination of the nation's water supplies from any of a long list of contaminants. The Safe Drinking Water Act ("SDWA") and its many amendments, mandate the testing for nearly a hundred chemicals and bacterium. The most commonly discussed targets of testing are lead, radionucleides, and coliform bacteria. A serious incident of coliform contamination occurred in Milwaukee in the recent past and highlighted the potential fatal consequences of bacterial contamination and of poor testing.
Where and how are samples obtained?
At each sample site a small sample (approx. 100ml) is drawn. Prior to taking the sample, most sample takers will run water for a short time to get "fresh" water and most will attempt some form of sterilization of the outlet nozzle - frequently by "flaming" the nozzle with a small torch.
Water suppliers generally have a choice of using existing water outlets, or of using dedicated sampling stations. If existing outlets are used, they are frequently:
- existing hydrants
- outside wall faucets
- public drinking fountains
- public restrooms
- private homes or businesses
The biggest problems experienced by suppliers who use existing water outlets are:
- access (weather, time of day, day of week, nobody home)
- control (other uses of the outlets can cause unpredictability)
- reliability (the supplier is actually inadvertently testing the plumbing of the sampling site, not just the supplier's system)
- using existing hydrants also runs the risk of introducing drain-hole contamination, bacteria from leather seals, lead from existing hydrant components and scaling and corrosion from the hydrant interior.
- sterilization techniques (usually "flaming" the outlet nozzle) are frequently not welcomed by private owners and are not practical on large-nozzle existing hydrants.
Dedicated sampling stations are chosen because they solve the problems of access, control, reliability, external contamination, acceptance and practicality.