Pool tile guide Houston hard water and your pool.

How hard is Houston water?

The City of Houston's 2025 water quality report gives an average hardness of 135.5 mg/L (about 7.9 grains per gallon) for the main system, which is in the hard range, with samples from 43.5 to 229 mg/L. The main system drew about 90% of its water from lakes and rivers that year and about 10% from deep wells.

Houston Public Works says east-side customers tend to get more surface water and west-side customers more well water. Some areas, like Kingwood, run on separate groundwater systems.

The suburbs are a different story

Outside the city, many communities rely more on groundwater from the Gulf Coast Aquifer, or on a blend of well water and surface water from regional authorities. Sugar Land, for example, has historically pumped most of its water from deep wells and added a surface water plant in 2013. Magnolia's city wells pump from the Jasper aquifer. The Woodlands blends Lake Conroe water with deep groundwater.

Groundwater generally carries more dissolved minerals than lake water, so pools on well-heavy supply often build calcium faster. Our service area pages go into each city.

Why evaporation matters more than you think

In a Houston summer a pool can lose a lot of water to evaporation, and every top-off brings in more minerals. The water in the pool gets more concentrated over time, and the excess comes out as scale at the waterline. That's why even pools on softer water eventually get a white line.

What you can do

Keep your chemistry balanced, keep the water level steady, and brush the waterline weekly with a soft nylon brush. When scale is already hard and crusty, bead or media blasting removes it without draining the pool.

Sources: City of Houston 2025 Water Quality Report; Houston Public Works: where your water comes from; City of Sugar Land water FAQ; SJRA Woodlands water supply.