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• Anthracite 0.8 to 2.0 millimeters
• Sand 0.4 to 1.0 millimeters
• Garnet 0.2 to 0.4 millimeters

Multimedia filters are generally designed with flux rates of 3 to 5 gallons per minute per square foot of surface area. Three filter medias, one on top of the other, provide the possibility to filter a larger distribution of solid sizes. The filters need to be backwashed when they are loaded with a typical amount of solids. Backwash is generally based on a solids load per unit of area between 2 to 3.7 kg/m² (0.5 to 0.75 lbs/ft²). A fixed number is hard to give as it depends on susceptibility to clog the filter, which may be higher when iron like particles are present.

The rate at which the filter is operated is always a hot topic. In general, a higher filter rate produces a higher SDI in the output. This SDI is of great importance in predicting filterability when membrane systems are present downstream such as sulfate removal packages and SWRO. Experience indicates that a velocity of 8-9 m/h (25 to 30 ft/h) gives acceptable values. When no membrane is present downstream 15 m/h (50 ft/h) is a conservative value. Higher rates may be possible, but small particle removal becomes significantly more difficult as rate increases.

Filter backwash facilities should be capable of expanding the filter bed by 50%. Rates of between 10 to 20 gallons per minute per square foot filter area are often used. Filter downtime during backwash typically averages 10 to 20 minutes including a wash period.

Microfiltration and Ultrafiltration are developing options for pretreatment to remove fine suspended particles. The advantage of membrane filtration is the reduction of size and weight when compared to traditional multimedia filtration.