Summary of Colorado's Water Reuse Guideline or Regulation for Centralized Non-potable 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.
On this page:
- Technical basis
- Applications of centralized non-potable reuse approved for use in Colorado
- Water reuse category/type
- Additional context and definitions
- Centralized non-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, centralized non-potable reuse The use of recycled water for centralized non-potable reuse where the water does not derive from the same site where it is to be reused. Can include, but is not limited to, toilet flushing, dust control, soil compaction, fire protection, commercial laundries, vehicle washing, street cleaning, snowmaking, and other similar uses. Excludes on-site non-potable water reuse and the use of recycled water for agriculture or landscaping. applications include toilet and urinal flushing, fire protection, vehicle washing and zoo operations among others. The source of water treated municipal wastewater Treated wastewater effluent discharged from a centralized wastewater treatment plant of any size. Other terms referring to this source of water include domestic wastewater, treated wastewater effluent, reclaimed water, and treated sewage. is specified by the state as domestic 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 approves the use of reclaimed water for centralized non-potable reuse applications including toilet and urinal flushing, fire protection, commercial laundries, zoo operations, construction and road maintenance and vehicle washing (5 Code Colo. Regs. § 1002-84). All applicable provisions of the Clean Water Act (CWA) (33 U.S.C. §§ 1251 et seq.), including its implementing regulations, must be met in addition to any state water quality standards. Reclaimed water is divided into four categories (Category 3 Plus, Category 3, Category 2 and Category 1) that have E. coli, turbidity, TSS and/or virus removal specifications. Category 3 Plus is the only category that requires virus removal (5-log reduction of enteric viruses). The technical basis for this virus reduction is not explicitly specified.
The E. coli standard was set based on the EPA’s 1986 Ambient Water Quality Criteria for Category 1 and 2 uses of reclaimed water (the decision to use the 1986 EPA standards was made in 2000, prior to EPA’s 2012 updates). While the Category 1 and 2 uses do not directly correlate to swimming in water, the Water Quality Control Commission found this to be an acceptable level of risk and assumed criteria established to protect swimmers will be more protective than individuals casually exposed to reclaimed domestic wastewater. For Category 3 uses, the E. coli standard is 0 detected in at least 75 percent of samples and not to exceed 126/100 mL in monthly samples, due to the higher risk of unintended cross connections and public contact (5 Code Colo. Regs. § 1002-84).
Turbidity is used as a surrogate measure of “microbial purity” (in regards to viruses and parasites) in reclaimed domestic wastewater and a “middle ground” of 5 NTU (in no more than 5% of results per month) was selected for the application of reclaimed domestic wastewater (5 Code Colo. Regs. § 1002-84). For centralized reclaimed water used for toilet and urinal flushing, a minimum 0.2 mg/L chlorine disinfection residual is required to reduce the risk of Legionella exposure.
Applications of centralized non-potable reuse approved for use in Colorado
5 Code Colo. Regs. § 1002-84 defines the following approved centralized non-potable reuse applications of reclaimed water treated by centralized reclaimed water systems:
- Toilet and urinal flushing (Category 3 Plus)
- Fire protection
- Residential fire protection (Category 3)
- Non-residential fire protection (Category 2)
- Commercial laundries (Category 2)
- Vehicle washing, automated and manual (Category 2)
- Construction and road maintenance (Category 1)
- Zoo operations, including the care of captive animals (Category 1)
Treatment requirements for these end use applications are the same for both centralized municipal and onsite water sources in Colorado. These same end use applications are housed in the Onsite Non-Potable Reuse summary for reclaimed water treated by localized systems instead of centralized systems.
Water reuse category/type
The various classes of treatment are defined by their respective treatment requirements and applicable performance standards. The respective treatment requirements are briefly summarized for centralized non-potable reuse applications:
- For Category 3 Plus reclaimed water, the treatment requirements are secondary treatment with filtration and disinfection. The filtration must be performed with conventional filtration; direct filtration; membrane, bag or cartridge filtration (in accordance with 5 Code Colo. Regs. § 1002-11); or alternative filtration technologies that are third-party tested to reliably remove 99.9% of challenge particles that are 3 microns at most. The disinfection must provide a minimum 5-log inactivation of viruses using either free chlorine or monochloramines, or a minimum UV of 40 mJ/cm2.
- For Category 3 reclaimed water, the treatment requirements are secondary treatment with filtration and disinfection. Category 3 water has an E. coli requirement of zero detections in the last 75% of samples (each calendar month) and ≤126 E. coli/100 mL (single sample maximum).
- For Category 2 reclaimed water, the treatment requirements are secondary treatment with filtration and disinfection. Category 2 water has an E. coli requirement of ≤126 E. coli/100 mL (monthly geometric mean) and ≤235 E. coli/100 mL (single sample maximum).
- For Category 1 reclaimed water, the treatment requirements are secondary treatment with disinfection. Category 1 water has an E. coli requirement of ≤126 E. coli/100 mL (monthly geometric mean) and ≤235 E. coli/100 mL (single sample maximum).
Additional context and definitions
In Colorado, reclaimed water is defined as “domestic wastewater that has received secondary treatment by a domestic treatment works (centralized or localized system) and such additional treatment as to enable the wastewater to meet the standards for approved uses” (Colorado WQCC, 2007). This summary focuses on domestic wastewater treated by centralized systems; the domestic wastewater treated by localized systems is discussed in the separate summary for Onsite Non-potable Reuse applications.
Domestic reclaimed water users must notify the public via sufficiently sized signs in all use areas, tanks and other equipment used for storage or distribution of reclaimed domestic wastewater that warn that reclaimed water is being used and is not safe for drinking (5 Code Colo. Regs. § 1002-84). All new or replaced piping, valves, outlets and other appurtenances must be marked to differentiate reclaimed water from potable water or other piping systems. An approved cross connection control device or method must be provided at all potable water service connections to reclaimed water use areas.
Centralized non-potable reuse specifications
Summary of Colorado's Centralized Non-potable Reuse Specifications
| Recycled Water Class/Category | Source Water Type | Water Quality Parameter | Specification | Sampling/Monitoring Requirements (Frequency of monitoring; site/ location of sample; quantification methods)* |
|---|---|---|---|---|
|
Category 3 Plus (toilet and urinal flushing) |
Domestic wastewater |
Chlorine disinfection residual |
≥0.2 mg/L chlorine disinfection residual |
1 grab sample/week |
|
UV dose |
≥40 mJ/cm2 |
Disinfection requirement |
||
|
Enteric viruses |
5-log inactivation |
|||
|
E. coli |
0 detected in at least 75% of samples (per calendar month) ≤126 E. coli/100 mL (single sample maximum) |
4 grab samples per 7 days |
||
|
Turbidity |
≤3 NTU (monthly average) 5 NTU (cannot exceed in more than 5% of results per month) |
1 reading per 12 hours of operation |
||
|
Category 3 (residential fire protection) |
Domestic wastewater |
E. coli |
0 detected in at least 75% of samples (per calendar month) ≤126 E. coli/100 mL (single sample maximum) |
4 grab samples per 7 days |
|
Turbidity |
≤3 NTU (monthly average) 5 NTU (cannot exceed in more than 5% of results per month) |
1 reading per 12 hours of operation |
||
|
Category 2 (non-residential fire protection, commercial laundries, vehicle washing) |
Domestic wastewater |
E. coli |
<126 E. coli/100 mL (monthly geometric mean) ≤235 E. coli/100 mL (single sample maximum) |
2 grab samples per 7 days |
|
Turbidity |
≤3 NTU (monthly average) 5 NTU (cannot exceed in more than 5% of results per month) |
1 reading per 12 hours of operation |
||
|
Category 1 (construction, road maintenance, zoo operations) |
Domestic wastewater |
E. coli |
<126 E. coli/100mL (monthly geometric mean) ≤235 E. coli/100 mL (single sample maximum) |
1 graba sample per 7 days |
|
Total suspended solids (TSS) |
30 mg/L (daily maximum) |
Source = 5 Code Colo. Regs. § 1002-84; Colorado WQCC, 2007
* Information about sampling and monitoring requirements such as frequency, site and quantification methods not specifically listed in the table was not explicitly specified in the State-specific regulations.
a Grab or composite samples may be used for total suspended solids analysis.
Upcoming state law or policy
No upcoming regulations pertaining to centralized non-potable reuse were found for Colorado.
References:
Clean Water Act, 33 U.S.C. §§ 1251 et seq.
Colorado Department of Public Health and Environment Water Quality Control Commission (WQCC). 2007. WQCC Water Quality Policy (WQP) - 25 Monitoring and Reporting Requirements for Reclaimed Water Treatment Facilities.
Reclaimed Water Control Regulation, 5 Code Colo. Regs. § 1002-84.
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.