Urban infrastructure and use of mass balance models for water and salt

Urban infrastructure supplies water to urban areas and drains away sewage and stormwater. These services are critical to the health and prosperity of modern cities. The built infrastructure includes reservoirs, concrete channels, canals, pipes, pumps, and treatment facilities. This infrastructure is usually owned by public entities (cities or water and sewer agencies). Some smaller sized systems are operated by private companies who can adequately train personnel and achieve economies of scale through operating facilities for several localized treatment and distribution systems. Privatization for operations of large-sized water and wastewater systems (i.e., serving >100,000 people) is slowly expanding in the USA, although the cities still own the infrastructure. Public entities bill private residences, commercial and industrial users, etc. to repay the enormous capital investment of this infrastructure, reoccurring replacement and repair and continuous operating expenses.