A water storage system comprising a tank having a first inclined or conical floor at the bottom of the tank, a second inclined or conical floor above the first inclined or conical floor, dividing the tank into upper and lower compartments, one or more inlet(s), an overflow outlet, a first draining outlet located at the sloping end of the first inclined floor or at the convergence of the first conical floor, a second draining outlet located at the sloping end of the second inclined floor or at the convergence of the second conical floor, and a consumer supply outlet located above the second inclined floor or above the second conical floor, wherein the upper compartment holds potable-grade water and the water from the lower compartment is reserved for fire fighting needs and used for non-potable purposes with periodic replenishment from upper compartment