Collecting a Representative Sample

Water testing measures key parts of a water system quality and chemistry to make sure the water treatment program is working properly. It is important when taking water samples that the sample represents the whole system and not a smaller, non-representative portion of the system. If a sample isn’t representative of the whole system, or if it is handled improperly, it can “lie to you”. By this we mean the test results will be true of the sample, but not the entire system and could lead to decisions affecting the water treatment program. Improper handling can consume certain chemicals or introduce contaminants which affect tests and your response to the result. An important key to a representative sample, is flushing the sample line before you take your sample. This will clear out impurities or chemical concentrations at the sample point.

You can learn a lot from your sample. By looking for clues in your samples, you can get a head start on understanding what is going on in the system. Look for things like color, smell and quality (cloudiness or suspended solids). Was the sample line clogged? These observations can help direct your testing.

Finally, in certain situations a chain of custody – that is, a record of who took or handled a sample, and when, is important for regulatory or legal reasons. In these cases, proper sampling and records are critical.

Collecting your sample

Once you have selected your sampling point, follow flushing guidelines and grab a sample. Doing this properly helps you prepare it for testing. If testing boiler water, be sure to cool the sample to room temperature before testing. You can use a sample cooler or cold-water bath to achieve this. Mistakes happen when testing, so be sure to collect a large enough sample to allow for repeat testing if needed.

  • Use a clean, non-reactive bottle. Also, make sure you have a cap so you can properly seal the container.
  • Clear contaminates in the bottle by rinsing at least three times with the water sample to be tested. This will ensure the sample bottle is clean.
  • Fill the bottle to the brim and overflowing to remove any air from the bottle and cap it. This keeps the sample fresh and removes air that can change the sample over time.
  • Label your bottle with sample location and application


Now that you’ve collected your sample (and cooled it if necessary), it’s important to test immediately! This is particularly important when testing sulfite. Following these sample collection fundamentals will ensure you get your testing started on the right track.

If you’re looking for more training, check out AquaPhoenix Academy, our online training classes to help grow and develop your team as well as a library of testing videos to help reinforce testing fundamentals.