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What are the main sources of water used by public water-treatment plants?

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Diagram of a water treatment plant showing the process from water inlet through mixing, coagulation, flocculation, settling, filtering, chemical treatment with chlorine, storage, and high-lift pumping to the distribution system. — water purification Water from inlets located in the water supply, such as a lake, is sent to be mixed, coagulated, and flocculated and is then sent to the waterworks for purification by filtering and chemical treatment. After being treated, the water is pumped into water mains for storage or distribution.

Public water-treatment plants primarily rely on two main categories of natural water sources: surface water and groundwater.12

Surface Water

Surface water is a common source for large cities and includes rivers, lakes, creeks, and streams. Because these sources are exposed to the atmosphere and human activity, they are often polluted with suspended silt, organic material, and microbes, requiring more extensive treatment—such as clarification and disinfection—to ensure they are safe for consumption. When natural flow rates are insufficient, communities may construct dams to create reservoirs, which store water for use during droughts.12345

Groundwater

Groundwater is frequently used by smaller towns and individual homes. It is typically extracted from aquifers via wells or infiltration galleries. Because groundwater undergoes natural filtration as it moves through soil and rock, it generally contains fewer microbes and suspended solids than surface water, though it may have higher concentrations of dissolved minerals.2634

In regions where freshwater is scarce, some treatment plants also utilize oceans and saltwater seas, employing desalination processes to produce potable water.31