Texas Drinking Water Quality: Hard Water, Nitrates, Arsenic, and Infrastructure
Texas water quality varies more by region than almost any other state. The large urban utilities, Dallas-Fort Worth, Houston, Austin, and San Antonio, have substantial resources and generally maintain compliance. Rural Texas and small municipal systems face more challenges, and the state’s geology creates some contaminant problems that have nothing to do with treatment quality.
Hardness: One of the Hardest States in the US
Texas is consistently ranked among the hardest-water states. The numbers depend on source and utility, but these are typical ranges:
San Antonio: 16-22 grains per gallon. El Paso: 12-18 gpg. Dallas: 10-14 gpg (varies by blending). Austin: 10-15 gpg.
For comparison, Boston area water runs 1-3 gpg. Seattle comes in under 1 gpg. Moving to San Antonio from Portland or Seattle is a significant adjustment, and the mineral deposits on faucets and appliances within weeks of moving make the hardness impossible to miss.
The source: the Edwards Aquifer, which supplies San Antonio and parts of central Texas, runs through limestone and dolomite. High calcium and magnesium content are inherent to the geology. The Colorado River (which supplies Austin) runs through similar terrain.
At 16+ gpg, water heater scale buildup is substantial without treatment. Scale inside tank water heaters reduces efficiency and shortens lifespan measurably. Dishwashers and washing machines also accumulate scale at high hardness levels. Texas households above 12 gpg benefit from a water softener in ways that residents in most other states don’t.
Arsenic in West Texas
Naturally occurring arsenic is elevated in parts of the Permian Basin, communities drawing from the Ogallala Aquifer in the Panhandle, and some areas of West Texas near the Rio Grande. This is a geology issue: specific rock formations in arid western Texas release arsenic into groundwater over time.
The EPA’s MCL for arsenic is 10 ppb. The MCLG is 0, meaning no safe level has been established. Some small Texas water systems have applied for compliance variances while installing treatment infrastructure. Private well owners in West Texas should specifically include arsenic in any water test panel.
Treatment: reverse osmosis certified to NSF/ANSI 58 removes 94-99% of arsenic at the point of use. Activated alumina specifically targets arsenic and is also used in whole-house configurations. Standard carbon filters do not remove arsenic. See our arsenic guide for the details.
THMs in Surface Water Systems
Houston and other large Texas utilities that rely on surface water, particularly reservoirs and river sources with high organic content, generate trihalomethanes (THMs) when they add chlorine for disinfection. THMs form when chlorine reacts with organic material. They’re unavoidable in chlorination-based treatment of surface water with high organic load.
Several Houston-area systems have been cited for elevated THM levels. The EPA MCL for total THMs (TTHM) is 80 µg/L. Long-term exposure above the MCL has been associated with increased bladder cancer risk in multiple epidemiological studies.
This doesn’t mean Houston water is unsafe in the short term. It means it’s worth knowing whether your specific system has had violations. Check the EWG Tap Water Database or your utility’s Consumer Confidence Report. If your system has elevated THMs, an NSF 53-certified activated carbon filter at the tap reduces disinfection byproducts. NSF 58 RO handles them as well. See our THMs page for the full picture.
Nitrates in Agricultural Areas
The Panhandle and South Texas Plains are heavily agricultural. Nitrogen fertilizer applied to cotton, corn, and grain sorghum dissolves in irrigation water and leaches into shallow aquifers. Private well owners near Lubbock, Amarillo, and agricultural South Texas, particularly around the Rio Grande Valley, should test nitrates annually.
The EPA MCL for nitrates is 10 mg/L. This is a hard limit for infants under 6 months, for whom nitrates above that level can cause methemoglobinemia. Reverse osmosis (NSF 58) removes nitrates. Boiling does not, and actually concentrates them.
The 2021 Winter Storm
The February 2021 winter storm that paralyzed Texas caused widespread pipe bursts and treatment plant failures, resulting in boil-water notices across hundreds of communities. At one point, roughly 13 million Texans were under boil-water advisories.
The event exposed a fundamental vulnerability: Texas water infrastructure was not designed for extended hard freezes. Treatment plants lost power or froze. Distribution lines failed. The Texas Commission on Environmental Quality (TCEQ) has since implemented new winterization requirements for water systems, but the infrastructure is aging in many communities and cold-weather resilience remains uneven.
What to Do
For urban residents on major utilities, the EWG Tap Water Database and your utility’s annual Consumer Confidence Report cover the documented issues. TCEQ publishes compliance data at tceq.texas.gov.
For well owners: test hardness, nitrates, arsenic, and bacteria at minimum. In West Texas, arsenic is the priority. In agricultural areas, nitrates. Hardness affects everyone.
At typical Texas hardness levels (10+ gpg), a water softener protects appliances and plumbing. At Dallas-Fort Worth hardness, the math on appliance lifespan usually justifies the investment within 4-6 years. In San Antonio, even faster. For drinking water specifically, an NSF 58 RO at the kitchen tap handles arsenic, THMs, and hardness minerals simultaneously. See our well water testing guide if you’re on a private well and need to know where to start.
For more on the contaminants most relevant to Texas: hard water, trihalomethanes, and arsenic in well water.