Mine is filtered through coal and gravel and a stainless steal wire mesh basket....mine was probably built in the 40's and collects water from the gutters. The water is usually used to just water and wash vehicles...now I watched a episode on this old house for a island in bermuda(I think) that the whole house water supply is from the cistern and is filtered by a whole house water filtering system and the town water supply is basically filtered at a pumping station...my well water is pumped/filtered through a water softener system ...now on the same show(this old house)they showed giant plastic containers that were placed in the ground taking the place of a cistern and then it was filtered(cartridge filters) and use to supplement the water supply for the house...www.kleenwater.com