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Computer software error causes surface water treatment violation

TCEQ Public Notice

Post Date:01/13/2020 3:30 PM

The City of Pflugerville received a Notice of Violation on January 10, 2020 from the Texas Commission on Environmental Quality (TCEQ) as the result of a computer programming error at the Surface Water Treatment Plant. As a result of the computer error, during a period of approximately 2.5 hours, the filtration membrane had a decay rate of .35 pounds per square inch (PSI) per minute which exceeds the state and federal guideline of .33 PSI per minute.

During a routine Membrane Integrity Test (MIT) on December 24, the Surface Water Treatment Plant alert notification software incorrectly indicated that a plant filtration membrane’s integrity was within acceptable levels and “passed” the automated test. As a result of the computer programming error, a filtration membrane that failed its MIT remained in service producing water for a period of 2.5 hours or less.

While reviewing the daily reports approximately 5 hours later, the City’s water operator discovered the computer programming error. The filtration membrane was immediately shut down, assessed and manually tested. The membrane was put back online after a successful retest showed all filtration measurements within state and federal guidelines.

As a result of this MIT computer programming error, less than 2% of the City’s daily gallon water usage, approximately 80,000 gallons out of six million produced that day, was potentially impacted. There were no issues indicated in other filtration or water treatment protocols. Immediately following this incident, the turbidity level, which is measure of the clarity of the water and a secondary measure of the membrane effectiveness, was compliant with TCEQ, state and federal requirements.

“The City’s top priority is the health and safety of its citizens, therefore for additional redundancy, city staff has implemented the requirement that water operators confirm manually that all testing functions meet TCEQ standards regardless of the computer display,” City Manager Sereniah Breland said. “In addition, the City has ordered an independent third-party test of Pflugerville water to restore consumer confidence and provided additional water reports on our website to show that our plant continues to produce water that meets or exceeds federal and state guidelines.”

The treatment violation does not mean cryptosporidium is present. The violation relates to a failed MIT which is one of several indicators of the effectiveness of filtration provided by the membranes if cryptosporidium were to be present in the water supply. The State of Texas requires that all occurrences of cryptosporidiosis be reported by medical staff to the county health department. According to Travis County Health Department data, in 2019 Travis County had 52 reports of cryptosporidiosis and two of those came from medical offices located in Pflugerville. If any resident is concerned about their health, they are encouraged to contact their medical provider.

The City is committed to public health and safety meeting all state and federal guidelines for drinking water. A public notice is being mailed to all City of Pflugerville, Manville Water Supply Corporation and Windermere Utility water customers. For additional information, frequently asked questions and copies of recent City water reports, please visit  The City Council will discuss this item on January 14 in the public Worksession. View the meeting live online at