Water is essential for the production of food and energy, human and ecosystem health, and much more. Our clean water needs range from the water we drink to the water we use to wash clothes. The American Water Works Association reported in their 1999 Residential Water Use Summary that the daily indoor per capita use in a typical American single-family home with no water-conserving fixtures is 74 gallons (or 27,010 gallons per capita) annually. Much of that water utilized within the home is transported to a local wastewater treatment plant (WWTP) where it must be brought to specific standards before it is discharged to receiving waters. Treating the wastewater properly requires knowledge of the population using the service (i.e. influent flow rate), the influent wastewater characteristics (e.g. biological oxygen demand, nitrogen, phosphorous, etc), and the point of discharge. The result is an energy intensive process that should be optimized according to the flow rate and specified standards.
The systems that provide treated water supply and treated wastewater seek to protect human and ecological health, but they also contribute to the depletion of non-renewable resources, the production of solid waste and emissions to the atmosphere, land, and water as shown in the following diagram.