The volume of liquid that passes through a given area in a specified time. Usually expressed as gallons per square foot per minute (or hour).

Flow in gallons per minute (GPM) through one square foot of filter medium. For residential pools, the filtration rate should be 2 GPM per square foot of D.E. filter surface area and 1 GPM per square foot of cartridge filter surface area. For most commercial pools, the filtration rate should be 1 GPM per square foot of D.E. filter surface area and .375 GPM per square foot of cartridge filter surface area.

The rate of water pumped through a filter, in gallons per minute (gpm). ATE VALVE: The type that spins "lefty-loosey; righty-tighty".

The speed at which the water is travelling through the filter. It is expressed in litres per minute per square metre of filter area or in kilolitres per hour per square metre.