City of Dover obtains its water from the Pend Oreille River through a dedicated raw water intake and delivery system. Raw water from the river is treated using a slow sand filtration system that can produce a maximum of 200 gallons per minute. More information regarding the water treatment system can be found in the article that was published at the time the system was first constructed (click here) or the City of Dover Facility Plan.
Slow sand filters work through the formation of a millimeter thin biofilm that forms on the top of the sand (called a “Schmutzdecke”. The Schmutzdecke is the layer that provides the effective purification in potable water treatment. As water passes through the Schmutzdecke, particles of foreign matter are trapped in the biofilm and dissolved organic material is adsorbed and metabolised by the bacteria in the biofilm. The water produced from a well-managed slow sand filter can be of exceptionally good quality with 90-99% bacterial reduction. The City of Dover operates four sand filter beds.
A dedicated treatment line then delivers the water to a baffled water treatment reservoir. Distibution lines the deliver the treated water from the reservoir to individual residences and businesses as well as fire hydrants through Dover.