The Ground Water Rule (GWR)

What is the Ground Water Rule (GWR) and How Does it Relate to the Total Coliform Rule (TCR)


EPA issued the Ground Water Rule (GWR) to improve your drinking water quality and provide additional protection from disease-causing microorganisms. Your drinking water comes from source water locations such as:

  • Lakes
  • Rivers
  • Reservoirs
  • Ground water aquifers

Water systems that have ground water sources may be susceptible to fecal contamination. In many cases, fecal contamination can contain disease causing pathogens. The GWR provides increased protection against microbial pathogens.

The GWR applies to Public Water Systems that serve ground water.  The rule also applies to any system that mixes surface and ground water if the ground water is added directly to the distribution system and provided to consumers without treatment.  The GWR was signed on October 11, 2006 by EPA Administrator Stephen L. Johnson. It was published in the Federal Register on November 8, 2006.

GWR Final Requirements:
The targeted, risk-based strategy addresses risks through an approach that relies on four major components:

  • Periodic sanitary surveys of systems that require the evaluation of eight critical elements of a public water system and the identification of significant deficiencies (e.g., a well located near a leaking septic system);
  • Triggered source water monitoring when a system (that does not already treat drinking water to remove 99.99 percent (4-log) of viruses) identifies a positive sample during its Total Coliform Rule monitoring and assessment monitoring (at the option of the state) targeted at high-risk systems;
  • Corrective action is required for any system with a significant deficiency or source water fecal contamination; and
  • Compliance monitoring to ensure that treatment technology installed to treat drinking water reliably achieves 99.99 percent (4-log) inactivation or removal of viruses.

What is the Groundwater Rule (GWR) and how does it relate to the TCR?  The purpose of the GWR is to provide for increased protection against microbial pathogens in PWSs that use ground water sources.  The GWR specifically identifies and targets ground water (GW) systems that may be susceptible to fecal contamination and requires a corrective action for GW systems with confirmed fecal contamination and/or significant deficiencies.  The GWR builds upon the TCR by addressing the risk associated with consuming water from a fecally- contaminated GW source.

A GW system must conduct triggered source water monitoring when the PWS is notified of a positive total coliform (TC) sample in the distribution system.  This monitoring allows the system to determine whether or not the positive TC sample was due to well contamination or a distribution system-related issue.

GWR Compliance Samples: GWR samples are collected at all groundwater source(s) prior to any treatment (i.e., raw water).  There are two types of GWR samples:

1.  Triggered source water monitoring:  These samples are collected from the source water in response to a routine distribution total coliform positive sample that was collected as part of the TCR.

  • The purpose of triggered source water monitoring is to evaluate whether the presence of total coliform in the distribution system is due to fecal contamination in the ground water source.
  • This type of source water monitoring is triggered by routine total coliform monitoring required by the TCR.
  • Since TCR monitoring is conducted regularly, triggered source water monitoring can occur at any time and thus provides an ongoing evaluation of ground water sources.

2.  Source water assessment monitoring:  These are raw water samples collected from the source water in response to a corrective action, hydrogeologic sensitivity assessment, or any assigned Department-required monitoring.

Source Water Monitoring for PWS

GWSs that do not provide, and conduct compliance monitoring for, at least 4-log treatment of viruses (through inactivation and/or removal) and do not purchase 100% of their water (and therefore have a source at which to sample) are notified of a total coliform-positive routine sample collected in compliance with the TCR (40 CFR 141.21) must conduct triggered source water monitoring.

  1. GWSs must collect at least one ground water source sample from each source in use at the time the total coliform-positive sample was collected.
  2. Samples must be collected within 24 hours of being notified of the total coliform positive sample.
  3. Sample must be taken before treatment or at a State-approved location after treatment.
  4. The triggered source water sample must be analyzed for the presence of one of three fecal indicators, E. coli, enterococci, or coligphage, as specified in the rule.
  5. The Fecal Indicator MBL analyzes for is E. coli via Colilert.

The diagram below represents an appropriate sampling location for triggered source water monitoring.

GWSs should have a sample tap at each source that enables triggered source water monitoring.


GWR Diagram

If the triggered source water sample is fecal indicator-positive, the GWS must either take corrective action, as directed by the state, or if corrective action is not required by the state and the sample is not invalidated by the state, the GWS must conduct additional source water sampling.

If the state does not require corrective action in response to a fecal indicator-positive triggered source water sample, the GWS must collect five additional source water samples (from the same source) within 24 hours of being notified of the fecal indicator-positive sample.
States may waive the triggered source water monitoring requirement if the state determines and documents, in writing, that the total coliform-positive routine sample is the result of a documented distribution system deficiency.

The following resources are taken from the EPA and can help you understand the Ground Water Rule Requirements further.  For more resources visit the EPA’s Ground Water Rule Resource Page directly.

EPA GWR Factsheet - Monitoring Requirements

EPA GWR Factsheet: Monitoring Requirements

     EPA Ground Water Rule Factsheet:  Monitoring Requirements

  • What is the Ground Water Rule?
  • What are the Source Water Monitoring Requirements?
  • What are the Compliance Monitoring Requirements?
  • What are the Compliance Deadlines Associated with GWR Monitoring?
  • What are the Monitoring Violations Associated with the GWR?


EPA GWR - Quick Reference Guide

EPA GWR: A Quick Reference Guide

     EPA Ground Water Rule:  A Quick Reference Guide

  • Overview of the Rule
  • Public Health Benefits
  • Critical Deadlines and Requirements
  • Analytical Methods for Source Water Monitoring
  • Major Provisions


EPA GWR Compliance Monitoring

GWR Compliance Monitoring

     EPA Ground Water Compliance Monitoring:  A Quick Reference Guide

  • Overview of the Rule
  • Purpose of Compliance Monitoring
  • When is Compliance Monitoring Required?
  • What are the Compliance Monitoring Requirements for Chemical Disinfection?
  • What are the Compliance Monitoring Requirements for Membrane Filtration?
  • Summary


EPA GWR Triggered & Representative Monitoring

EPA GWR Triggered & Representative Monitoring

     GWR Triggered & Representative Monitoring:  A Quick Reference Guide

  • Overview of the Rule
  • Purpose of Triggered Source Water Monitoring
  • Triggered Source Water Monitoring Requirements
  • Sampling at Representative Sources and Trigged Source Water Monitoring Plans
  • Variations in Requirements Based on System Size
  • Invalidation of Fecal Indicator-Positive Samples
  • Exceptions to the Trigged Source Water Monitoring Requirements
  • Notification Requirements


EPA GWR Sample Collection & Transport

EPA GWR Sample Collection & Transport

     EPA GWR Sample Collection & Transport:  A Quick Reference Guide

  • Overview of the Rule
  • GWR Situations Requiring Sample Collection and Transport
  • Sampling Location
  • Sample Collection:  Containers & Procedures