Houston sits on soft sediment rather than bedrock, a thick layer of clay, sand, and silt deposited over millions of years by rivers flowing into the Gulf of Mexico. Underground water trapped in aquifers holds that sediment in place.

Since the 1890s, Houston has been pumping water out of its underground aquifers. As the city grew through the 20th century, demand for groundwater increased, and the ground began to compact. By the mid-20th century, parts of the Houston-Galveston area had sunk by ten feet or more.

A study published in the journal Nature Cities in May 2025 confirmed that Houston is the fastest-sinking major city in the United States. The study found that more than 42 percent of the Houston metropolitan area is subsiding at a rate greater than five millimeters per year, and twelve percent is sinking faster than ten millimeters per year. In some suburbs between Katy and Fulshear, the ground has been measured dropping more than three centimeters per year.

Subsidence occurs because the aquifers beneath Houston are not underground lakes or caves. They are layers of sand, gravel, and clay saturated with water. The pressure of that water holds the particles apart. When water is pumped out, the pressure drops, and the particles compact. Clay layers, once compacted, do not re-expand. The ground does not come back up.

Houston was also drained from below by the petroleum industry. Oil and gas extraction works on the same principle as groundwater extraction. Removing pressurized fluids from underground formations causes the ground above to compact. For much of the 20th century, both processes ran simultaneously.

The most dramatic result occurred around Baytown, about 25 miles east of Houston. Between 1906 and 1978, the land there subsided by more than ten feet. Coastal farmland became open water, and industrial infrastructure had to be raised or relocated.

In 1975, the Texas Legislature created the Harris-Galveston Subsidence District to regulate groundwater extraction. The solution was to switch from groundwater to surface water from rivers and reservoirs. In areas where this mandate was applied, it worked. Downtown Houston and the industrial zones along the ship channel largely completed the transition by the 1990s, and subsidence rates in those areas slowed significantly.

But the regulatory district covered Harris County and Galveston County. By the time it was created, Houston’s metropolitan area had already expanded beyond those boundaries. In Fort Bend County, Montgomery County, Waller County, and Brazoria County, rapid growth in the 2000s and 2010s was built largely on groundwater, which was cheaper and faster to connect than surface water systems. The problem migrated outward into the fastest-growing areas of the region.

Hurricane Harvey in August 2017 exposed part of the cost. The storm stalled over Houston for nearly four days, releasing rainfall that exceeded the capacity of weather instruments in the area. Some locations recorded sixty inches of rain. The result was $125 billion in damage, the costliest natural disaster in American history at the time. More than 36,000 homes were destroyed or declared uninhabitable, and more than one hundred lives were lost in Texas.

A post-Harvey study found that 85 percent of the areas that flooded had been actively subsiding before the storm arrived. Subsidence lowers the ground unevenly, so drainage channels engineered for a flat landscape may no longer direct water away properly. Roads that once shed rainwater begin to hold it, and detention basins lose their capacity.

Damage from subsidence is visible in cracked foundations, buckled sidewalks, and doors that no longer close properly. Foundation repair is an active industry in the Houston area, with homeowners routinely spending tens of thousands of dollars on steel piers to hold structures in place while the ground continues to move. The most costly damage is underground. Water mains, sewer lines, and gas lines bend and crack when the ground moves unevenly, and the failure may not be visible until a sinkhole opens or a road collapses.

The Harris-Galveston Subsidence District has expanded its regulatory reach and tightened conversion mandates. Water utility districts in the western suburbs are under orders to complete their transition from groundwater to surface water. A major surface water project is under construction to pull treated water from Lake Houston and push it westward through new pipelines. When complete, it will slow ongoing subsidence caused by current groundwater extraction.

It will not reverse what has already happened. The clay layers compacted over eighty years of groundwater withdrawal will not re-expand. The ground that has sunk is gone permanently.

Houston is taking steps to address the problem, though belatedly and partially. The city continues to grow, and the decisions being made now about where to build neighborhoods, what infrastructure standards to require, and how to enforce groundwater conversion timelines will determine how much further the ground settles. The scientists studying the subsidence, the engineers building the pipeline, and the regulators enforcing the rules are all doing necessary work. A public that understands what is happening beneath the city will be better positioned to make informed decisions about its future.