Our drinking water comes from two sources: surface water and groundwater. Surface water is water stored above ground, such as in a river or lake. Groundwater is the water beneath Earth’s surface in underground aquifers. In the greater Houston area, sustained pumping and withdrawal of groundwater causes land subsidence.
Land subsidence is sinking of the land surface. Pumping large amounts of groundwater causes the ground to settle, lowering the elevation of the land. From 1906 to 2000, as much as seven feet of subsidence has been measured in northwest Harris County.
Groundwater withdrawal in Harris and Galveston counties is regulated by the Harris-Galveston Subsidence District (HGSD), a special purpose district created by the Texas Legislature in 1975 for the purpose of reducing land subsidence. In general, the HGSD requires all water suppliers in Harris and Galveston counties to reduce groundwater pumping based on the rate of subsidence in their area. Areas 1 and 2 are required to primarily use surface water. Area 3 is mandated to convert to 80 percent surface water supply by 2035. Most of the City of Houston has already converted from groundwater to surface water. Now, surrounding areas must follow suit in meeting these regulatory mandates.
The WHCRWA provides service to a large portion of Area 3, which is still largely dependent on groundwater. To comply with the conversion requirements of the HGSD, the WHCRWA is delivering the Surface Water Supply Project (SWSP). This project will help to reduce land subsidence and will meet the water needs of a rapidly growing population.