You are the CPO for a large municipal swimming pool with a volume of 560,000 gallons and an average daily bather load of 1300 people. How often should you backwash the high rate pressure sand filters?

Backwashing high rate pressure sand filters is crucial for maintaining optimal performance and water clarity in a municipal swimming pool system. The correct choice is based on the differential pressure readings between the influent and effluent gauges of the filter system.

When the difference in pressure between these gauges reaches 10 to 20 psi, it indicates that the filter has become sufficiently dirty and needs to be cleaned to restore its efficiency. This pressure differential signifies that the flow of water is being restricted due to the accumulation of contaminants and debris within the sand filter media. Regularly monitoring this pressure difference allows for timely backwashing, which helps to maintain water quality, reduce the risk of contamination, and ensure proper filtration.

Other response options suggest fixed schedules for backwashing, such as daily, weekly, or monthly intervals. However, such approaches may not necessarily align with actual filter performance or the specific condition of the filter media. Backwashing based solely on time rather than pressure gauge readings could lead to either premature backwashing, wasting water and resources, or inadequate cleaning, which could compromise water quality. Therefore, basing backwashing frequency on the gauge differential is the most effective practice for maintaining filter efficiency and ensuring a safe and clean swimming environment.