Houston, TX water hardness: 135.5 mg/L average (about 7.9 gpg), range 43.5–229
The City of Houston's 2025 Water Quality Report gives total hardness for the Main System (the largest of its six systems, by our reading of the report's customer counts), as 43.5–229 mg/L, average 135.5 mg/L (about 7.9 gpg, our conversion). The average is hard on the USGS scale. The range runs from soft to very hard.
Test your tap before you set a softener, because Main System water ranged from 2.5 to 13.4 gpg in 2025.
Which of the six City of Houston systems you are on
Your bill names the system. Most Houston customers are on the Main System. The report covers six separate public water systems.
| System | Source (per report) | Customers | Avg mg/L | Range mg/L | Avg gpg* | Range gpg* | Year; PDF page |
|---|---|---|---|---|---|---|---|
| Main System | 90.3% surface water (Lake Livingston/Trinity River; Lake Conroe and Lake Houston/San Jacinto River), 9.7% groundwater (104 wells) | 2.97M | 135.5 | 43.5–229 | 7.9 | 2.5–13.4 | 2025; p. 9 |
| Kingwood | 100% groundwater (16 wells, Evangeline and Chicot aquifers) | 80.3K | 124 | — | 7.3 | — | 2025, one sample; p. 11 |
| Willow Chase | 100% groundwater (5 wells) | 15.2K | 163.5 | 160–167 | 9.6 | 9.4–9.8 | 2025; p. 13 |
| District 73 | 100% groundwater (2 wells) | 6.9K | 97.4 | — | 5.7 | — | 2025, one sample; p. 15 |
| District 82 | 100% groundwater (2 wells) | 951 | 107 | — | 6.3 | — | 2024, one sample; p. 17 |
| Belleau Woods | Purchased from City of Humble (mixed surface and groundwater) | 439 | 129 | — | 7.5 | — | 2025, one sample; p. 19 |
Why Houston's Main System range is so wide
The Main System blends surface water from three lakes with groundwater from 104 wells deeper than 750 feet. The all-groundwater systems in the table run 97–167 mg/L, while the Main System's lowest reading is 43.5. That pattern fits softer lake water and harder well water, but the report does not give hardness by plant, source or neighborhood. The only way to know where your tap sits in 43.5–229 mg/L is to test it.
What this means at home
Test your tap first, then set appliances by your result.
Test before you set a softener in Houston
Main System water ranged from 2.5 to 13.4 gpg in 2025. Test your tap first. If you can't, use 14 gpg, which covers the 2025 maximum. For a closer setting, test a few times over a season and program the highest reading. 14 gpg may waste salt if your area gets mostly lake water. On Willow Chase water (about 9.4–9.8 gpg), program 10 gpg. Belleau Woods reported iron at 0.64 mg/L in one sample. If your softener has an iron setting, follow its manual.
The dishwasher level Houston homes should pick
For the Main System average (about 7.9 gpg, ≈ 7.6 °dH), pick the manual's level for 7–9 gpg. Move up one level if glasses show white film. Move down if you see etching or cloudiness that does not wipe off and you know your water is soft.
How much scale kettles and fixtures get
At the 2025 average, expect steady white scale in kettles and coffee makers and on shower glass. Homes near the high end will need to descale more often.
Other water systems in the Houston area
Many Houston-area homes are served by municipal utility districts (MUDs) or other cities, each with its own report. The City's report covers only the six systems above. Check the name on your water bill.
Sources
- City of Houston, Houston Water Quality Report 2025 (PDF), pages 9–19: https://houstonpublicworks.org/sites/g/files/nwywnm456/files/doc/003_2025_houston_water_quality_report.pdf
- Houston Public Works, Drinking Water Quality Report page (all years): https://houstonpublicworks.org/drinking-water-quality-report
- USGS Water Science School, Hardness of Water: https://www.usgs.gov/water-science-school/science/hardness-water