Which condition might warrant an increase in the flow rate of a rapid rate sand filter?

Increasing the flow rate of a rapid rate sand filter is often necessary during the backwashing process. Backwashing is a method used to clean the filter by reversing the flow of water through the sand bed, which dislodges trapped debris and contaminants. This process requires a higher flow rate to effectively agitate the sand and carry the dislodged materials out of the filter.

Achieving the right flow rate during backwashing helps ensure that the filter is thoroughly cleaned and can function effectively once normal filtration resumes. If the flow rate is too low during backwashing, the debris might not be adequately removed, leading to reduced filtration efficiency and potentially a shorter lifespan for the filter media.

Other choices, such as low pressure in the pump or high water clarity, do not necessitate an increase in the flow rate, but rather indicate different operational responses. Winterization typically involves preparing the pool and its equipment for cold weather, not adjustments to the filtration flow rate. Thus, backwashing is the scenario where increasing the flow rate is essential for optimal filter performance.