Water Hardness in Houston

Houston's tap water averages around 137 mg/L of calcium carbonate — roughly 8 grains per gallon — according to Houston Public Works' annual water quality reporting. That places the city in the "hard" band, though notably softer than the Texas cities to its west: San Antonio and Dallas are both substantially harder.

The supply is a blend. Most of Houston's water is surface water drawn from Lake Houston, Lake Conroe and the Trinity River system, supplemented by groundwater from the Gulf Coast aquifer. The two source types have different mineral profiles: the surface water is moderately mineralised, while groundwater moving through the region's calcium-rich coastal sediments picks up considerably more hardness. Houston has been shifting progressively from groundwater toward surface water for decades, partly to address subsidence caused by aquifer withdrawal — a shift that has moderated hardness in parts of the system.

This creates an important distinction that catches people out: the city figure of roughly 8 grains per gallon applies to the City of Houston system. Many surrounding municipal utility districts in the greater Houston area operate their own wells and report hardness of 15 grains per gallon or more — nearly double. If you are outside the city system, in one of the numerous suburban MUDs, your water is likely harder than this page's figure and the relevant number is your own district's report.

At 137 mg/L within the city, scale accumulates steadily but not aggressively — expect to descale a kettle every few months and to run a dishwasher on a moderate salt setting. Houston's heat and heavy air-conditioning load mean water heaters work hard year-round, so periodic flushing is worthwhile even at this moderate hardness level.