Drinking Water Testing

Overview

NTMWD conducts thousands of tests each month in a state-certified laboratory to ensure drinking water safety, and those results are reported to the Texas Commission on Environmental Quality (TCEQ).

Additionally, TCEQ conducts routine water sampling in the NTMWD and city systems through an independent laboratory to confirm water quality compliance with state and federal standards. The cities we serve also collect their own water samples, which are analyzed in NTMWD's state-certified laboratory and reported to TCEQ.

NTMWD's water meets all safety standards required by the TCEQ, EPA, and the Safe Water Drinking Act. Test results are available for the public to review in our monthly and annual water quality reports. The cities and utilities we serve also produce their own water quality reports.

Chlorine

Only chlorine-based disinfectants are approved by the EPA for secondary water disinfection. These included chloramine (ammonia + chlorine) and free chlorine. EPA requires water treatment facilities to maintain a minimum chlorine level of 0.5 milligrams per liter (mg/l)-or 0.5 parts per million (ppm)-during normal operations and a maximum running average of 4 mg/l (or 4 ppm).

A noticeable presence of chlorine does not mean the water is unsafe. Some people can sense (through taste or smell) chlorine concentrations as low as 1 ppm.

During the annual temporary change in disinfectant, NTMWD posts chlorine levels from samples taken at the three points where water leaves the Wylie Water Treatment facilities. Cities and local providers monitor levels within their local distribution systems. Chlorine levels in local systems should be lower than the levels leaving the treatment plant. 

Review real-time average daily total chlorine (mg/L) leaving the Wylie Water Treatment Plants.

Disinfection By-Products

Disinfection By-Products (DBPs) form when disinfectants, like chlorine, react with naturally occurring compounds in the water. All commonly used disinfectants form DBPs. The EPA regulates DBPs (Trihalomethanes or THMs and Haloacetic acids or HAA5) at levels that current research considers safe. NTMWD's use of ozone and chloramine for disinfection reduces the DBPs regulated by the EPA and TCEQ.

NTMWD and TCEQ test results confirm that DBP levels are well within the acceptable ranges the EPA considers safe. NTMWD tests for DBP monthly, an increased frequency from the regulation.

You can review monthly independent lab testing results for DBPs in our monthly water quality reports. These reports are typically uploaded to the website by mid-month for the previous month. 

View DBP independent results prior to 2023 inclusion in the monthly water quality reports.