Many human activities interact with the water cycle at various phases. They do not necessarily remove water from the cycle, but they do hold volumes of water at various points before returning it. For example, thermoelectric power plants, including those using coal, nuclear fuel, and natural gas to generate electricity, withdraw surface water to cool power plants. Depending on the arrangement of the plant, this water is returned heated back to surface water sources or recirculated within the plant until decommissioning and then returned to the source.
Drinking water is also a temporary withdrawal, either from reservoirs and rivers at the surface or underground aquifers. Municipalities with dozens to millions of water customers constitute public water supply systems. Rural populations and individual homesteads may instead receive their water from private wells or cisterns. After use, municipalities collect water with sewage systems. These systems usually include large scale chemical and microbial treatment facilities, which return water to a high level of cleanliness before returning it to the water cycle.
Many scientists consider water to be removed from the water cycle in the emerging case of deep subsurface disposal. Operators are injecting produced water, wastewater, and hydraulic fracturing fluids deemed too expensive or too inconvenient for treatment and subsequent return to their sources. These disposal methodologies are engineered to permanently sequester fluids far beneath underground sources of drinking water in containing formations that will not allow the fluids to migrate to other underground water sources or to the surface. When the injection water is initially drawn from surface or groundwater sources, this water is removed permanently from the water cycle.
Images: “ecological problems” by De Visu via Shutterstock.com; “Injection Well” by J. Veil, Argonne National Laboratory; “Illustration” by Top Energy Training
