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Groundwater Rule

The Groundwater Rule protects your drinking water quality and provides additional protection from disease-causing microorganisms.

Water systems that have groundwater sources may be susceptible to fecal contamination which can contain disease causing pathogens. The Groundwater Rule (GWR) provides increased public health protection against microbial pathogens. The GWR applies to all public water systems (PWS) that provide groundwater, except; 

  • combine all their groundwater with surface water prior to treatment,
  • treat all their groundwater to 4-log standards (99.99% inactivation of viruses),
  • treat all their groundwater to Groundwater Under the Influence of Surface Water (GUI) standards (enhanced treatment).

Systems that treat their groundwater to Surface Water or GUI standards would follow the Surface Water Treatment Rule found in §290.111. Systems that provide 4-log treatment are exempt from the Corrective Action (CA) requirements in §290.116.

The GWR is found primarily in 30 Texas Administrative Code §290.109 and §290.116 and may be found in Title 30 of the Texas Administrative Code (TAC) Chapter 290 Subchapter F: Drinking Water Standards Governing Drinking Water Quality and Reporting Requirements for Public Water Systems . TCEQ regulatory guide, Coliform Monitoring, Analyzing, and Reporting Guide (RG-421), provides detailed information on total coliform and E. coli compliance related to the Revised Total Coliform Rule (RTCR) and the GWR.

Major Rule Components

Triggered Source Monitoring

Triggered Source Monitoring (TSM) is defined as raw groundwater source monitoring required for systems that do not provide at least 4-log treatment (99.99% inactivation) of viruses when a routine distribution coliform sample is positive under the RTCR. A groundwater system must collect, within 24 hours of notification of the routine distribution total coliform-positive sample, at least one raw groundwater source E. coli (or other approved fecal indicator) sample from each groundwater source in use at the time the distribution coliform-positive sample was collected. If any well(s) were not in use at the time of the routine distribution positive sample, please complete and submit the  Groundwater Rule Notification of Inactive Well(s) for Triggered and Assessment Source Monitoring (TCEQ Form 20891).

TSM is intended to be a one-to-one relationship between routine distribution positives and raw well samples required. If you have more than one well, below are some examples about how many raw well samples must be collected.  

  • A PWS that has two active wells (A and B) and collected one positive routine sample (Site 1) must collect one raw well sample from each well.
    • A total of two raw samples must be collected, one from well A and one from well B.
  • A PWS that has two active wells (A and B) and collected two positive routine samples (Site 1 and Site 2) must collect two raw well samples from each well.
    • A total of four raw well samples must be collected, two from well A and two from well B.

The Microbial Reporting Form (MRF) (TCEQ Form 10525) is required when reporting coliform sample results to TCEQ for compliance with the RTCR and GWR. How to complete the MRF (video 16 minutes) and  Instructions for Completing the TCEQ Microbial Reporting Form (TCEQ Form 10525/INST) provides guidance to the sample collector and labs about how the MRF must be completed. The lab will provide the MRF to the PWS. You can see an example and other useful information in the  RTCR Repeat Requirements Diagram.

See What To Do After You Receive A Total Coliform Positive on a Routine Distribution Sample for additional required actions and information.

Representative well monitoring is allowed if the system has an approved Triggered Source Monitoring Plan (TSMP). For more information on TSMPs please contact the GWR program at The TSMP Checklist D, TSMP Checklist H and How to Develop a Monitoring Plan for a Public Water System (RG-384) contain additional TSMP requirements and guidance.

Assessment Source Monitoring

Assessment Source Monitoring (ASM) is defined as raw groundwater source monitoring required by the TCEQ based on groundwater source susceptibility to fecal contaminants. ASM may be required as a condition of a rule exception under the Technical Review and Oversight Team (TROT) or as a corrective action (CA) under the GWR. For more information email or visit the Requesting an Exception to Rules and Regulations for Public Water Systems webpage. For more information on ASM as a CA please contact the GWR Program at

Texas Drinking Water Public Laboratory Map

TCEQ has developed the following map to help you locate NELAP accredited public laboratories across the state of Texas that offer microbial coliform testing. Use the map below to find a laboratory near you and their contact information. Always call laboratories to confirm their address, sample drop off hours, and prices.

  • To find additional laboratory information, view the Texas Drinking Water Public Laboratories Map and the PWS Laboratory Map Table found in the PWSSP webpage.

Comprehensive Compliance Investigations and Significant Deficiencies

A sanitary survey is an onsite review of a public water system's adequacy for producing and distributing safe drinking water. TCEQ Regional staff perform Comprehensive Compliance Investigations (CCI) to meet the EPA's sanitary survey requirement. Significant deficiencies (SD) cause, or have the potential to cause, the introduction of contamination into water delivered to customers. If an SD is identified during a CCI then the system must correct the SD under the GWR.

CCIs are conducted for community systems every three years and noncommunity systems every five years. If the TCEQ identifies an SD during a CCI, the groundwater system must take corrective action. If a TCEQ investigator identifies an SD during a CCI the system must correct the SD through the regional investigator to prevent a violation under the GWR. If an SD is not corrected within 120 days or the timeframe allowed by an approved corrective action plan and schedule the system will receive a violation under the GWR.

4-log Treatment

4-log treatment is defined as at least 99.99% (4-log) treatment of viruses using inactivation, removal, or an executive director-approved combination of 4-log virus inactivation and removal. 4-log treatment can be used as a compliance option under the GWR to be exempt from TSM or 4-log treatment may be used by TCEQ as a corrective action for wells that are susceptible to fecal contamination. Keep in mind that if a system implements 4-log treatment voluntarily and later wants to discontinue the treatment and resume TSM for compliance, then the system must request to discontinue the treatment in writing. To discontinue 4-log treatment contact TROT at For systems that treat drinking water to at least 99.99 percent (4-log) inactivation or removal of viruses, the rule requires compliance monitoring to ensure that the treatment technology installed is reliably inactivating and removing contaminants. Systems can claim 4-Log treatment by providing a Concentration-Time (CT) Study for approval by the TCEQ and then maintain 4-Log treatment through daily or continuous residual monitoring (depending on population) and documenting this using the 4-log Groundwater Monthly Operating Report. The Concentration-Time Study For Water Treatment Plants, webpage has guidance and useful documents such as the ExcelGroundwater Minimum Specified Residual (GWMSR) Template, Selection of Baffling Factors and Operation Conditions for T10 Calculations, and ExcelGroundwater 4-Log Monthly Operating Report (TCEQ Form 20362).

Corrective Action

When a system has a significant deficiency or a fecal indicator-positive groundwater source sample the TCEQ requires the groundwater system to implement one or more of the following corrective action options:

  • correct all significant deficiencies (e.g., repairs to well pads and sanitary seals, repairs to piping tanks and treatment equipment, control of cross-connections);
  • provide an alternate source of water (e.g., new well, connection to another PWS);
  • eliminate the source of contamination (e.g., remove point sources, relocate pipelines and waste disposal, redirect drainage or run-off, provide or fix existing fencing or housing of the wellhead);
  • provide treatment that reliably achieves at least 4-log treatment of viruses (using inactivation, removal, or a state-approved combination of 4-log virus inactivation and removal);
  • well disinfection in accordance with American Water Works Association procedures (additional guidance available in RG-554 PWS: Groundwater Source Disinfection); or 
  • a state-specified period of ASM.

Public Notice Requirements

All public notices for the RTCR violations, including the acute E. coli maximum contaminant level violation, can be found at Public Notice Language for Drinking Water Compliance, under Microbial Violations.

2020 Public Drinking Water Conference Presentation

GWR Compliance and CT Studies presentation covers triggered source monitoring and plans, assessment source monitoring, significant deficiencies, Concentration Time (CT) Studies and 4-log treatment.

Assistance and Helpful Links

TCEQ's Drinking Water Watch holds the information we have for your public water system and is open to the public. This has contact information, sample sites, sample results, violations, and public notice due dates.

TCEQ's Financial, Managerial, and Technical (FMT) Assistance program offers free financial, managerial, and technical assistance to help public water and wastewater systems comply with regulations.

TCEQ's Revised Total Coliform Rule provides increased public health protection against microbial pathogens

EPA Groundwater Rule