In water management, municipal wastewater is that which almost exclusively contains contamination from human excreta. Small portions from commercial and industrial use are converted into population equivalents (PE) to obtain comparability.

Because wastewater contains many different components and the expense for analysis to determine each individual substance would be inefficient, the composite parameters COD and BOD (chemical and biochemical oxygen demand) are generally used. Municipal wastewater carries COD concentrations of 400 to 600 mg/l and the COD to BOD ratio is about 2. Statistically speaking, each connected resident produces 60 g of BOD content per day.

The main portion of contaminants are organic substances. In household wastewater, they consist of up to 40% nitrogen compounds such as urea and protein, up to 50% carbohydrates and up to 10% fats.

Specific water use per resident varies widely worldwide. In Germany, for example, an average of 150 liters per resident is calculated. This level depends greatly upon individual lifestyle habits and the standard of water-consuming appliances (washing machine, dishwasher, etc.).