A swimming pool’s turnover rate may be considered the most important aspect of a commercial swimming pool. It is simply how fast the volume of an entire pool can go through a circulation system.
What is it?
Let’s say you have a 100,000-gallon lap pool. To “turn it over”, which is to say circulate the water, you need to move the entire pool through your filter system. The amount of time it takes to do this is “turnover”. So, if it takes six hours to do it, the turnover rate is six hours.
This does not mean that your entire pool is going through the filter system, just the volume of the pool. If you run 100,000 gallons through the filter system, a lot of that water is coming through again and again. The truth is that you need to turnover the pool multiple times a day to get as much of the water as possible. Hence why turnover rate requirements are so strict.
Why is it important?
Your pool must meet the minimum regulated turnover rate. The most common modern requirement for a lap pool is six hours and much less for spas, splash pads, etc. This varies so please consult your local regulations.
This number is not random. The faster the turnover rate, the safer the pool. Contaminated water needs to be moved through the system for proper filtration and treatment. A low turnover rate is dangerous for swimmers! In commercial aquatics, this turnover rate is required 24/7, not just when there are swimmers. In inspector can shut down a pool not meeting minimum turnover rates.
How to determine pool turnover rate?
The flow rate is the key to determining the turnover rate and why flow meters on the main line are required by all regulations. If you know the volume and the flow rate, that’s all you need:
Volume ÷ Flow Rate ÷ 60 = Turnover Rate
If a pool is 100,000 gallons and has a flow rate of 300 then the turnover rate is less than 6 hours (5.555 hours)
Dead Zones
It was mentioned that just because the turnover rate is 6 hours or less, does not mean that the entire pool is going through the filter system. There are parts of many pools where the circulation is less than optimal. This would be corners, stairs, water features, anything that interrupts normal circulation. These areas are more prone to contamination and that is why you may notice more staining and issues in these areas. Brush these areas! Brushing the pool not only cleans those surfaces but can aid in circulation immensely.
Always remember the importance of the turnover rate. Many factors can cause it to no longer meet the minimum required. If the sand filters have not been backwashed in a long time, or the pump is damaged and not functioning properly, or there’s debris in the pipes restricting flow rate, or many other scenarios. Check the flow rates frequently to ensure that the body of water is still meeting the minimum turnover rate.