How fast does water move through a slow sand filter?
A slow sand filter is a dynamic device and will change over time. The amount of time it takes water to flow through a slow sand filter will depend on the size of the sand, the depth of the sand, how long the filter has been in operation after initial start up or after the most recent cleaning, the depth of water above the surface of the sand, the area of the sand surface, and the turbidity of the input water. The filters described in this study have flow volumes that vary from 3 litres per hour ( after 1 year of running without wet harrowing ) to 45 litres per hour ( after 5 months of operation without wet harrowing ). The sand in these filters described here typically holds 50 percent water by volume – approximately 100 litres. So the simple math tells us that it takes anywhere from about 2 hours (almost too fast) to about 30 hours ( more than slow enough ) for the water to flow through the filters described here. This is approximate time. More water on top of the sand will increase t
