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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 that provide groundwater, except public water systems that combine all their groundwater with surface water prior to treatment, systems that treat their groundwater to 4-log standards (99.99% inactivation of viruses), or systems that treat 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 would be 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 Adobe Acrobat PDF Document. TCEQ regulatory guide, application/pdfColiform Monitoring, Analyzing, and Reporting Guide (RG-421), provides detailed information on coliform (total coliform and/or E. coli) compliance related to RTCR and the GWR.

Major Rule Components

Triggered Source Monitoring

Triggered Source Monitoring (TSM) is defined as raw groundwater source monitoring required for systems not providing at least 4-log treatment (99.99% inactivation) of viruses when a routine distribution coliform sample is positive under the Revised Total Coliform Rule (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 document the inactive well(s) by completing and submitting the application/pdfGroundwater Rule Notification of Inactive Well(s) for Triggered and Assessment Source Monitoring Adobe Acrobat PDF Document (TCEQ Form 20891).

TSM is intended to be a one-to-one relationship between routine distribution positives and raw well samples required. At least one TSM sample is required for each routine distribution positive; for example, if a system collects two positives and has one well, then the system needs to collect two raw samples from the well.

The Microbial Reporting Form (TCEQ Form 10525) is required when reporting coliform sample results to TCEQ for compliance with the RTCR and GWR. It is important to fill out the Microbial Reporting Form properly to receive appropriate credit for completing the TSM requirement. application/pdfHow to Complete the Microbial Reporting Form has instructions for completing the MRF. The application/pdfRTCR Repeat Requirements Diagram provides needed sampling guidance.

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 application/pdfTSMP Checklist DAdobe Acrobat PDF Document, TSMP Checklist H Microsoft Word Document and How to Develop a Monitoring Plan for a Public Water SystemAdobe Acrobat PDF Document (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 executive director 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.

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 Groundwater Minimum Specified Residual (GWMSR) Template Microsoft Excel Document, Selection of Baffling Factors and Operation Conditions for T10 CalculationsAdobe Acrobat PDF Document, and Groundwater 4-Log Monthly Operating Report Microsoft Excel Document (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 AssociationExit the TCEQ procedures (additional guidance available in RG-554 PWS: Groundwater Source DisinfectionAdobe Acrobat PDF Document); 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 Adobe Acrobat PDF DocumentExit the TCEQ 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 RuleExit the TCEQ