League City's tap water had coliform bacteria in as many as 2.65% of samples during its worst month of 2025, according to the city's annual drinking water quality report.

That peak rate falls below the federal maximum contaminant level (MCL) of 5% of monthly samples. But the report also states that "coliforms were found in more samples than allowed," and it includes language describing a Level 2 assessment of the city's water system. The report does not spell out what triggered the assessment or what it found.

A separate entry in the report lists a 0.96% coliform-positive rate for July.

Under the Revised Total Coliform Rule enforced by the Texas Commission on Environmental Quality (TCEQ), a Level 2 assessment is a detailed study to identify potential causes of microbial contamination. It can be triggered by an E. coli MCL violation or by a second assessment trigger within a rolling 12-month period. Being required to complete one is not itself a violation, according to TCEQ.

Coliform bacteria occur naturally in the environment. Their presence does not mean the water is unsafe, but they serve as an indicator that other, potentially harmful bacteria may be present, the report states.

Where the water comes from

The report covers data collected from Jan. 1 through Dec. 31, 2025. League City buys surface water from two suppliers: Gulf Coast Water Authority, which draws from the Brazos River in Galveston County, and the City of Houston, which draws from the Trinity River in Harris County. The city also operates eight groundwater wells at sites across town.

TCEQ has assessed the city's source water and found some sources susceptible to certain contaminants, the report states.

Lead, disinfectants and other results

During the 2022-2024 lead and copper sampling period, the 90th-percentile lead level was 3 parts per billion. That is well below the federal action level of 15 ppb. One site exceeded the action level, with individual results ranging from 0 to 58 ppb. The report does not identify which site or what corrective steps were taken.

Chloramine, the disinfectant used in the system, averaged 2.39 milligrams per liter in 2025, within the allowed maximum of 4 mg/L. Total trihalomethanes, a disinfection byproduct, peaked at 46.9 ppb against a limit of 80 ppb.

The city also reported results from the EPA's fifth round of unregulated contaminant monitoring. Several per- and polyfluoroalkyl substances, known as PFAS, were detected at trace levels. No federal limits currently apply to those compounds.