Water resources include surface water sources like rivers and lakes as well as groundwater sources located underground. Surface water is replenished by precipitation and flows through river systems, while groundwater is located in aquifers below the water table. People use water resources for household needs, agriculture which accounts for 69% of water usage globally, industry, recreation, and environmental purposes. Water pollution can occur from point sources like waste water treatment plants or nonpoint sources like stormwater runoff, harming water quality.