Also Known As:

Influent water is the water that is entering the pool filter, as opposed to effluent water which is exiting the filter. The pipe or line that brings water into the filter system is called the influent or suction line. It’s important to remember the influent water has not been filtered.

The influent pressure gauge shows the pressure of the water inside the filter. It should be checked regularly. As the filter medium becomes dirty, it takes more pressure to push the water through the filter. For that reason, the pressure of the influent line can demonstrate whether or not the filter is dirty. The buildup of debris on the filter media continues to trap finer particles over time. Therefore, when pressure builds, smaller particles can be captured. There is a trade off, as higher pressure also reduces flow rate. When the difference between the influent and effluent pressure measurements are greater than the clean filter pressure by 7 to 10 psi (pounds per square inch), it’s time to backwash or clean the filter.

If a DE or sand-filter pool has a low flow rate and low influent pressure, the influent line may be blocked. Check skimmer baskets and clear them of any debris. If the pressure is still low, release valves on the influent line to push any obstruction through the pipe.