A water purifier includes a chamber having a perimetric wall, a bottom wall at a first end, and an opening at a second, opposed end. A collection pipe extends along the bottom wall. A siphon pipe fluidly coupled with the collection pipe extends along the perimetric wall away from the bottom wall. An exit pipe fluidly coupled with the siphon pipe extends through a perimetric wall discharge opening. A layer of granular material in the chamber contains and sustains a biological layer of microorganisms for reducing water-borne pathogenic microorganisms. An inorganic anti-microbial disinfectant source is incorporated into a portion of the granular material. The granular material and biological layer provide progressive biochemical remediation of pathogenic microorganisms. The inorganic disinfectant source provides progressive chemical and biochemical remediation of pathogenic microorganisms. Water containing pathogenic microorganisms percolates through the granular material, and flows into and discharges from the pipes as potable water.