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 Main System total hardness as 43.5–229 mg/L, average 135.5. The average is hard on the USGS scale. The range runs from soft to very hard.
All six City of Houston systems
The report covers six separate public water systems. Your bill names the system. Most Houston customers are on the Main System.
| 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. Hardness by neighborhood: not published. The only way to know where your tap sits in 43.5–229 mg/L is to test it.
What this means at home
Water softener
Houston is the city where testing matters most. Main System water ranged from 2.5 to 13.4 gpg in 2025. Test your tap a few times over a season, then program the highest reading. Without a test, 14 gpg covers the reported maximum but 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.
Dishwasher
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.
Kettles and fixtures
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.
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Not on City of Houston water?
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