Taking Water Samples
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. If you are getting satisfactory readings at the furthest point from the inlets (where the disinfectant is weakest), it stands to reason that you must have a satisfactory reading throughout the pool. If you took the sample from too close to the inlets, you may be led to believe that the disinfectant levels were satisfactory, but there is actually a chance that the disinfectant levels could deplete to below the recommended parameter by the time it got to the outlets.
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.
General Points on Pool Water Testing
- the equipment used should be clean and dry
- reagent tablets should not be touched as this would affect the reading
- COSHH assessments should be carried out on all reagent chemicals
- all samples should be taken from the same, pre-determined point every time
- staff should be trained in pool water testing
- pool testing and effective lifeguarding cannot be carried out at the same time
- photometers should be re-calibrated on an annual basis
- if results are not as expected, always do an immediate re-test
- put test tubes on a stable, flat surface when crushing the reagent tablets