Abstract: An aeration filtration tank and system for treating raw feed water includes a first tank or chamber and a second tank or chamber within the first chamber. An annular overflow platform is provided atop the second chamber and around the periphery of said platform are a plurality of weirs.Raw feed water enters a precipitation chamber at the bottom of the first chamber and flows slowly into the second chamber. As the water rises in the second chamber it is treated, as necessary, with fluid reagents and with air.Because the overflow platform is substantially larger in area than the cross sectional area of the second chamber, the water flows relatively slowly through the weirs and any gases entrained in the water are liberated. The gases are removed from the first chamber by an exhaust fan and conduit atop the first chamber.A small third tank within the first tank is fluidly connected with a conduit to withdraw clarified and purified water from the first tank.