A method of removing rosin soldering flux or other residues from a printed wiring board comprises directly adding to the wash water which contacts the boards a powdered cleaning composition which comprises water soluble alkaline salts. The method of directly adding the cleaning composition to the water supply in the form of a powder eliminates the need to incorporate organic stabilizers which previously have been required to maintain surfactants and the like in solution in aqueous concentrates. By reducing the organic content of the cleaning compositions, the aqueous effluents from the cleaning method have substantially reduced biological oxygen demand (BOD) and chemical oxygen demand (COD) levels.