What is the designed flow rate for a rapid sand filter?

The designed flow rate for a rapid sand filter is typically 2 gallons per minute per square foot (gpm/ft²). This rate strikes a balance between effective filtration and the need to maintain a reasonable hydraulic loading that allows the sand to perform its filtering function without creating excessive head loss or causing the sand media to become disturbed.

At this flow rate, the filter is able to effectively remove suspended particles while allowing for adequate backwashing and cleaning cycles when needed. Higher flow rates, such as 3 gpm/ft² or 5 gpm/ft², can lead to challenges in maintaining the clarity of the effluent water and may require more frequent maintenance interventions. Therefore, the choice of 2 gpm/ft² is widely recognized and adopted in water treatment practices, especially in the context of designing facilities capable of efficiently treating water.