Described is the determination of suspended solids in raw waters, waste waters and effluents by filtration. Colloidal matter may escape filtration and not be included in the reported value. The lower limit of the determination is 2 mg/l. Results obtained with unstable samples should be interpreted with caution. Floating oil and other inmiscible liquids will interfere. Samples containing more than about 1000 mg/l of dissolved solids may require special treatment.