Rapid sand filter

[2] The first modern rapid sand filtration plant was designed and built by George W. Fuller in Little Falls, New Jersey.

The filtration system requires a relatively small land area in proportion to the population served, and the design is less sensitive to changes in raw water quality, e.g. turbidity, than slow sand filters.

"[5][6] The unfiltered water flows at about 5 m/h, through the filter medium under gravity or under pumped pressure and the floc material is trapped in the sand matrix.

[1]: 9–11  Rapid sand filtration has very little effect on taste and smell and dissolved impurities of drinking water, unless activated carbon is included in the filter medium.

Rapid sand filters must be cleaned frequently, often several times a day, by backwashing, which involves reversing the direction of the water and adding compressed air.