Summary of Colorado's Water Reuse Guideline or Regulation for Potable Water Reuse

This page is part of the EPA’s REUSExplorer tool, which summarizes the different state level regulations or guidelines for water reuse for a variety of sources and end-uses.
The source water for this summary is Treated Municipal Wastewater.

• Technical basis
• Types of planned potable reuse approved for use in Colorado
• Water reuse treatment category/type
• Additional context and definitions
• Potable reuse specifications (table)
• Upcoming state law or policy
• References
• Disclaimer

This page is a summary of the state’s water reuse law or policy and is provided for informational purposes only. Please always refer to the state for the most accurate and updated information. 

In Colorado, potable water reuse potable water reuse The use of highly treated recycled water for drinking water purposes. This reuse application includes both indirect potable reuse through introduction of recycled water into an environmental buffer such as a surface reservoir or groundwater aquifer, and direct potable reuse through introduction of recycled water into a drinking water system. applications include direct potable reuse. The source of water (treated municipal wastewater) is specified by the state as treated wastewater. The write-up uses state terms when discussing sources or uses of water that may differ from the Regulations and End-Use Specifications Explorer's (REUSExplorer's) terms.

Technical basis

Colorado allows the use of treated wastewater for direct potable reuse (DPR) under the Direct Potable Reuse Rule in their Primary Drinking Water Regulations (5 Code Colo. Regs. § 1002-11-14). The Colorado DPR Rule specifies that DPR applies to systems that pipe treated wastewater directly from the wastewater treatment plant to advanced water treatment and does not pass through an environmental buffer. When wastewater effluent is discharged to a surface water body the DPR rule does not apply. Potable water in the United States must meet all applicable Safe Drinking Water Act (SDWA) requirements, including its implementing regulations (40 C.F.R. § 141) for chemical and microbial contaminants. An application and written approval by the Colorado Department of Public Health and Environment (CDPHE) is required for all DPR projects in Colorado (5 Code Colo. Regs. § 1002-11-14). The application requires a communications and outreach plan to inform consumers of the DPR project, an enhanced source water control plan, a DPR operations plan and at least one year of monitoring results. Department approval will specify conditions for such plans. The water supplier must comply with the treatment requirements and performance standards specified in 5 Code Colo. Regs. § 1002-11-14 as well as Colorado’s surface water requirements specified in 5 Code Colo. Regs. § 1002-11-8.

A water supplier may opt for one of two methods to determine the minimum log removal targets (LRTs) for pathogen control for their planned DPR system.

1. When sufficient data on pathogen concentrations in treated municipal wastewater effluent is not available and the process treating wastewater consists of “oxidized wastewater” defined by 5 Code Colo. Regs. § 1002-11-14(1), the combined DPR treatment processes must achieve specified log reduction targets. The specified log reduction targets are as follows: a threshold of 12-log₁₀ enteric virus reduction, 10-log₁₀Giardia lamblia cyst reduction and 10-log₁₀Cryptosporidium oocyst reduction. The LRTs are based on microbial (pathogen) concentrations in drinking water that would result in less than 1 infection per 10,000 people per year (Cal. Code Regs. tit. 22). If oxidized wastewater is not produced from a process that has a 10-day solids retention time, then pathogen characterization is mandatory to validate that the above LRTs are protective and would still result in a less than 1 infection per 10,000 people per year.

2. If a dedicated sampling program is in place, the supplier may determine alternate minimum LRTs based on expected pathogen concentrations in treated municipal wastewater effluent. However, the minimum LRTs cannot be less than 8-log virus reduction, 6-log Giardia reduction and 5.5 log Cryptosporidium reduction (CDPHE, 2023a). The minimum time frame and sampling frequency of pathogens is weekly collection for one year on a consistent schedule (e.g., Tuesdays at 3pm) to prevent bias from sampling events only during optimal treatment performance. Treated wastewater effluent samples must be collected from the point prior to advanced drinking water treatment processes for DPR (e.g., before aeration and disinfection) (CDPHE, 2023a).

For chemicals, wastewater characterization will be needed to develop a list of acceptable target chemicals. The supplier may recommend a list of potential target chemicals to be approved for a year-long wastewater characterization to be approved by the CDPHE. Chemicals may be designated as targets if their toxicity profile has been determined or re-evaluated, or if the compound requires multiple removal processes (e.g., 1,4-dioxane, PFAS and disinfection byproducts like NDMA). In addition, Total Organic Carbon (TOC) must be characterized in the treated wastewater for the application for DPR since it is correlated with recalcitrant contaminants in water (CDPHE, 2023a). Other considerations include:

• Chemicals with EPA health advisory levels (HALs) but not MCLs and chemicals with HALs and MCLs that are not defined by the U.S. EPA.
• Contaminants with domestic water supply standards included in the Colorado Water Quality Control Commission’s regulations 5 Code Colo. Regs. § 1002-31 for basic standards and methodologies for surface water) or 5 Code Colo. Regs. § 1002-41 for basic standards for ground water.
• Chemicals potentially hazardous or at unpalatable concentrations reported in (e.g., National Water Research Institute or peer-reviewed journals) but with toxicity and prevalence not yet widely corroborated can also be designated as targets (Marron, et al., 2019; Khan, Fisher and Roser, 2019)
• Additional contaminants including PFAS at a fire training area, petroleum hydrocarbons near a leaking underground fuel storage tank, metal plating or solvents at dry cleaners.

For indicator compounds such as artificial sweeteners that have similar chemical properties as other recalcitrant chemicals, the DPR treatment process should aim at removing a minimum of 75% of each indicator compound from the treated wastewater before finished water delivery. The number of indicator compounds will vary based on the number of target chemicals that could serve as indicators.

Types of planned potable reuse approved for use in Colorado

5 Code Colo. Regs. § 1002-11-14 defines the following approved potable uses of treated wastewater:

• Direct potable reuse

DPR is only approved for systems that pipe treated wastewater directly from the wastewater treatment plant to the DPR treatment facility (i.e., does not pass through an environmental buffer).

Water reuse treatment category/type

Colorado does not assign treated wastewater used for DPR to a specific treatment category or class. For all public water systems that use DPR, the supplier must comply with the treatment technique requirements at critical control points for pathogen reduction, and entry point and distribution residual disinfectant concentrations specified in 5 Code Colo. Regs. § 1002-11-14(7) and the treatment technique requirements for chemical critical control points specified in 5 Code Colo. Regs. § 1002-11-14(8). The supplier must use three separate critical control points for pathogen reduction at minimum. One critical control point must be for disinfection processes and one for filtration processes. A disinfection critical control point includes UV or ozone treatment. A filtration critical control point includes either (1) reverse osmosis, (2) conventional filtration (e.g., ozone and biofiltration) or (3) an alternative filtration process approved by the CDPHE 5 Code Colo. Regs. § 1002-11-14(7).

Additional context and definitions

5 Code Colo. Regs. § 1002-11-14(1) provides definitions of relevant DPR terms. Some definitions include:

• Direct potable reuse is defined as producing finished drinking water using a series of processes on treated wastewater that has not passed through an environmental buffer.
• Treated wastewater is defined as any wastewater treatment plant effluent that has received enhanced wastewater treatment or secondary wastewater treatment as defined in the Direct Potable Reuse Policy. At a minimum, these systems produce oxidized wastewater to achieve a defined source water quality for additional treatment by direct potable reuse suppliers.
• An environmental buffer is defined as a surface water or groundwater aquifer that dilutes or naturally attenuates pathogenic and chemical contaminants. Wastewater effluent from a permitted wastewater treatment plant that has been discharged to a surface water body is considered to have passed through an environmental buffer and therefore the DPR rule does not apply.
• A critical control point is defined as “a treatment process or a portion of a treatment process designed to reduce, prevent or eliminate a human health hazard.” (5 Code Colo. Regs. § 1002-11-14). A critical control point monitoring location is defined as “an approved location where effectiveness and status of each critical control point is monitored. Each critical control point must have at least one approved monitoring location.” (5 Code Colo. Regs. § 1002-11-14).

Colorado’s Enhanced Source Water Control Program Policy (CDPHE, 2023b) provides additional information on the program’s direct potable reuse requirements regarding Enhanced Source Water Control Plan submittals.

Potable reuse specifications

Summary of Colorado's Potable Reuse Specifications

Sources = 5 Code Colo. Regs. § 1002-11-14

^a When log reduction credits for each pathogen critical control point have been approved by the Department, the sum of log reduction values should be equal or greater than the values specified in the table. However, if a dedicated sampling program is in place, the supplier may determine an alternate minimum LRT based on expected pathogen concentrations from previously collected monitoring data. However, the minimum LRT may not be less than 8-log virus reduction, 6-log Giardia reduction and 5.5 log Cryptosporidium reduction.

^b CDPHE (2023a).

Upcoming state law or policy

No upcoming regulations related to potable water reuse were found for Colorado.

References:

Colorado Department of Public Health & Environment (CDPHE). 2023a. Direct Potable Reuse Policy, DW-016.

CDPHE. 2023b. Enhanced Source Water Control Program Policy, DW-017.

Direct Potable Reuse Rule, 5 Code Colo. Regs. § 1002-11-14.

EPA-Administered Permit Programs: The National Pollutant Discharge Elimination System, 40 C.F.R. part 122.

National Primary Drinking Water Regulations, 40 C.F.R. § 141.

Regli S, Rose JB, Haas CN, Gerba CP. 1991. Modeling the risk from giardia and viruses in drinking-water. J Am Water Work Assoc. 83:76-84.

Regulations Related to Recycled Water, Cal. Code Regs. tit. 22.

Surface Water Treatment Rule, 5 Code Colo. Regs. § 1002-11-8.

Surface Water Treatment Rule: Enhanced Treatment for Cryptosporidium, 5 Code Colo. Regs. § 1002-11-10.
 

Disclaimers

Please contact us at waterreuse@epa.gov if the information on this page needs updating or if this state is updating or planning to update its laws and policies and we have not included that information on the news page.