The rate of backwash water shall not be less than ________ of vertical rise per minute and usually not more than ________ of vertical rise per minute.

The rate of backwash water is a crucial aspect of maintaining effective filtration in water treatment processes. A backwash rate of 20 inches per minute ensures that the system effectively removes accumulated debris, sediment, and particulates from the filter media. This rate is effective enough to create sufficient turbulence, helping to lift and suspend the trapped materials so they can be flushed out of the system.

The upper limit of 35 inches per minute is typically recommended to avoid damaging the filter media while still providing effective cleaning. While higher rates can enhance cleaning efficiency, extremely high velocities might lead to the loss of filter media or potential structural damage to the filtration system. Thus, this range is established to balance efficient cleaning with the longevity and integrity of the filtration system.