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This investigation evaluated the important parameters required to achieve an acceptable infiltration rate with adequate water quality improvement in a soil wastewater treatment system. Locally available sand and Kanpur silt (Entisol) were used in this evaluation. The particle‐size distribution of soil was found to be an important parameter in improving the infiltration rate and water quality. An expression, based on retardant kinetics for biochemical oxygen demand (BOD), is proposed for chemical oxygen demand (COD) removal in soils as a function of soil depth. Also, an empirical relationship is developed that shows how the overall reduction in COD with soil depth varies with the time since the wasetwater application was initiated. The overall COD reduction rate increases for the first several days following the initiation of the wastewater application, and thereafter it decreases. This indicates that wastewater should not be continuously applied to soils. There should be alternating wet periods (wastewater application) and dry periods (no wastewater application). A significant reduction in NH3‐N, total N, total P, and total coliforms also resulted because of particle‐size distribution.