Swimming Pool Water Sampling: Where and Why

The point of water testing is to ensure that there is enough disinfectant in the water, (at the correct pH level) to kill the germs. Therefore, when taking samples, it’s important that you collect them from a spot within the pool that is most likely to have the lowest level of disinfection. That way, you can be reasonably confident that everywhere else will have enough disinfectant too.

Do not take the samples for routine testing from the sample point on the monitoring system in the plant room. This sample point is not intended for this purpose (it’s for calibrating the sensors in the monitoring equipment against a sample of water taken from the same location on the system as the sensors).

Pool water samples should be collected as far as possible away from the inlets. This is because the water returning to the pool from the plant room will have recently been injected with a fresh dose of disinfectant. Therefore, the water coming into the pool at the inlets will be relatively strong with disinfectant, while the water at the furthest point from the inlets will be relatively weak with disinfectant.

In terms of the correct depth, it is recommended that the sample should be taken from within the top 150mm of pool depth. This is where most of the pollution lies within the pool and is therefore representative of ‘worst-case scenario’. If you find that your disinfectant readings are satisfactory from within the most heavily polluted area of the pool, you can be reasonably confident that disinfectant levels will be satisfactory everywhere.

Once a sampling point has been identified, it’s generally best to be consistent about taking water samples from this point. This is so you can identify patterns and trends from the test results, ie.: disinfectant levels increasing or decreasing from test to test. If you were taking samples from different points every time, patterns and trends may not be identified. However, on a periodic basis, it can be beneficial to take samples take samples from various points around the pool to check that your regular sampling point is still representative of actual pool water conditions.

General Points on sampling:

  • the equipment used should be clean and dry
  • staff should be trained in pool water testing
  • pool sampling/testing and effective lifeguarding cannot be carried out at the same time
  • samples should be collected in a plastic beaker (not glass), example below


A sampling beaker for pool water testing.