The nature of wastewater is described by its flow and quality characteristics. Municipal wastewater is comprised of domestic wastewater, industrial wastewater, infiltration and inflow into sewer lines, and stormwater runoff. Domestic water usage, and the resultant wastewater, is affected by climate, community size, density of development, community affluence, dependability and quality of water supply, water conservation requirements or practices, and the extent of metered services. Wastewater quality can be defined by physical, chemical, and biological characteristics. Physical parameters include color, odor, temperature, solids, turbidity, oil, and grease. Solids can be further classified into suspended and dissolved solids as well as organic and inorganic fractions. Organic matter in wastewater can be related to oxygen demand and organic carbon measurements. Contaminants in municipal wastewater are introduced as a result of water usage for domestic, commercial, or institutional purposes; water usage for product processing or cooling purposes within industries discharging liquid effluents into municipal sewerage systems; and infiltration/inflow and/or stormwater runoff.