Summary of Colorado's Water Reuse Guideline or Regulation for Onsite Non-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 Onsite Collected Waters.
On this page:
- Technical basis
- Background on NSF/ANSI Standard 350
- Types of onsite non-potable reuse approved for use in Colorado
- Water reuse category/type
- Additional context and definitions
- Onsite 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, onsite non-potable water reuse The use of treated onsite collected waters for non-potable purposes at the single-building or district scale. This reuse application excludes the use of recycled water from a centralized treatment and distribution system for landscape irrigation or commercial uses. include irrigation, toilet and urinal flushing and vehicle washing, among others. The source of water onsite collected waters Water sources generated within or surrounding a building, residence, or district. Other terms referring to this source of water include onsite collected stormwater or rainwater, greywater, blackwater, air conditioning condensate, and foundation water. is specified by the state as graywater and domestic wastewater (i.e., blackwater). 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.
Check out Colorado's other onsite non-potable water reuse summary!
State requirements for water quality and treatment are often associated with the source water. Colorado has an onsite non-potable water reuse summary page where the source water is rainwater collected onsite.
Technical basis
Colorado approves the onsite non-potable reuse of graywater for subsurface irrigation and toilet and urinal flushing and domestic wastewater for industrial and commercial uses, landscape and agricultural irrigation, fire protection and toilet and urinal flushing (5 Code Colo. Regs. § 1002-86). 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. Treated graywater is categorized into four classes that vary by design flow requirement and reuse application. There are no treatment requirements for graywater reused onsite for subsurface irrigation. Onsite non-potable water reuse systems treating graywater for urinal and toilet flushing must comply with NSF/ANSI Standard 350 (CDPHE WQCC, 2019) and use a treatment technology that will be “protective of public health” without the need for on-going water quality testing. The Water Quality Control Commission found that the NSF/ANSI standard meets an acceptable technology review protocol that would be certified by a third-party agency to simplify the technology review process for the local jurisdictions (refer to more information).
Colorado also approves onsite non-potable reuse of reclaimed domestic wastewater (i.e., onsite treated blackwater) for industrial and commercial uses, landscape and agricultural irrigation, fire protection and toilet and urinal flushing (5 Code Colo. Regs. § 1002-84). The technical basis of pathogen removals is a health-based target of less than 1 infection per 10,000 people per year for Category 3 uses and 1 infection per 100 people per year for Category 2 and Category 1 uses. Category 1 and 2 health-based targets are less stringent than Category 3 because of “the low risk of exposure from unintended cross connections” (5 Code Colo. Regs. § 1002-84). Microbial (pathogen) log reduction values were derived via numerical simulation assuming raw sewage distributions reported in the literature with median densities of 103.9 norovirus gc/L, 102.3Giardia lamblia cysts/L and 101.6Cryptosporidium oocysts/L (Schoen et al., 2017). In addition to meeting the LRTs, the water quality standards for E. coli, turbidity and TSS must be met. For Category 1 and 2 uses of reclaimed water, the E. coli standard was set based on the EPA’s 1986 Ambient Water Quality Criteria for swimming (the decision to use the 1986 EPA Criteria 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 based on the assumption that 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 75 percent non-detect 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 more than 5% of results per month) was selected for the application of reclaimed domestic wastewater (5 Code Colo. Regs. § 1002-84).
Background on NSF/ANSI Standard 350
The National Sanitation Foundation/American National Standards Institute (NSF/ANSI) was originally adopted in 2011 and includes requirements for testing onsite residential and commercial water reuse treatment systems. NSF/ANSI 350 includes requirements for two categories of facilities: residential (up to 1,500 gallons per day) and commercial (systems exceeding 1,500 gallons per day); and four different types of influent: (1) combined black and gray water; (2) gray water only; (3) bathing water only; and (4) laundry water only. The standard covers general non-potable reuse applications, including surface and subsurface irrigation and toilet and urinal flushing. There are two categories of effluent criteria that vary slightly: Class R for single family residential and Class C for multi-family residential and commercial. These effluent quality criteria were developed using the currently existing guidelines codes and regulations, with the goal of meeting the majority of existing codes (although the guidelines do not meet all state codes). Class R includes E. coli water quality requirements not to exceed 14 MPN/100 mL geometric mean and 240 MPN/100 mL single sample maximum and Class C includes E. coli water quality requirements not to exceed 2.2 MPN/100 mL geometric mean and 200 MPN/100 mL single sample maximum.
Types of onsite non-potable reuse approved for use in Colorado
5 Code Colo. Regs. § 1002-86 defines the following approved onsite non-potable reuse applications for the use of treated graywater:
- Single family, subsurface irrigation (Category A graywater),
- Non-single family, subsurface irrigation (Category B graywater),
- Single family, indoor toilet and urinal flushing (Category C graywater),
- Non-single family, indoor toilet and urinal flushing (Category D graywater).
5 Code Colo. Regs. § 1002-84 defines the following approved onsite non-potable reuse applications for the use of domestic wastewater:
- Zoo operations (Category 1)
- Commercial laundries (Category 2)
- Vehicle washing, automated and manual (Category 2)
- Washwater applications (Category 2)
- Fire protection
- Non-residential fire protection (Category 2)
- Residential fire protection (Category 3)
- Toilet and urinal Flushing (Category 3)
- Resident-controlled landscape irrigation (Category 3)
- Resident-controlled food crop irrigation (Category 3)
Treatment requirements for these end use applications are the same for both centralized municipal and onsite water sources. There are additional end use applications allowed for localized treatment systems in Colorado, however, these applications are housed in other end use application summary documents (e.g., agricultural irrigation, landscape irrigation, industrial reuse, commercial and other non-potable and oil and gas production).
Water reuse category/type
The treatment requirements for graywater are briefly summarized for onsite non-potable reuse applications (5 Code Colo. Regs. § 1002-86):
- Category A and C graywater is limited to a design flow of 400 gallons per day or less. Category B graywater is limited to a design flow of 2,000 gallons per day or less. There is no maximum design flow for Category D graywater. The graywater treatment works for Category C and D water must be certified under NSF/ANSI Standard 350. Disinfection (a free chlorine residual of 0.2-4.0 mg/L) and dyeing are required as part of the treatment process.
The treatment requirements for onsite non-potable reclaimed domestic wastewater are briefly summarized for the allowed non-potable reuse applications (5 Code Colo. Regs. § 1002-84):
- For Category 1 reclaimed water, the treatment requirements are secondary treatment with disinfection. Category 1 water treated by localized systems has additional requirements for enteric viruses (6.0-log reduction).
- For Category 2 reclaimed water, the treatment requirements are secondary treatment with filtration and disinfection. Category 2 water treated by localized systems has additional requirements for enteric viruses (6.0-log reduction), parasitic protozoa (5.0-log reduction) and enteric bacteria (4.0-log reduction).
- For Category 3 reclaimed water, the treatment requirements are secondary treatment with filtration and disinfection. Category 3 water treated by localized systems has additional requirements for enteric viruses (8.5-log reduction), parasitic protozoa (7.0-log reduction) and enteric bacteria (6.0-log reduction).
Additional context and definitions
In Colorado, graywater for Categories A, B, C and D is limited to graywater collected from bathroom and laundry room sinks, bathtubs, showers and laundry machines (5 Code Colo. Regs. § 1002-86).
Onsite non-potable reuse of reclaimed domestic wastewater is limited to “domestic wastewater that has received secondary treatment by a domestic treatment works from a single building, multiple buildings within a single property or area bounded by dedicated streets or ways, or a district designated by a city or county for treatment to produce reclaimed water for beneficial use where the source water does not have meaningful inputs from industrial or other diluting sources” (localized system) and comprises Categories 1, 2 and 3 uses (5 Code Colo. Regs. § 1002-84).
Onsite non-potable reuse specifications
Summary of Colorado's 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 A graywatera (Single family, subsurface irrigation) |
Graywater |
No fit-for-purpose requirements for Category A graywater reuse |
||
|
Category B graywatera (Non-single family, subsurface irrigation) |
Graywater |
No fit-for-purpose requirements for Category B graywater reuse |
||
|
Category C graywatera (Single family, indoor toilet and urinal flushing) |
Graywater |
The graywater treatment works must be certified under “Class R” of NSF/ANSI 350 Onsite Residential and Commercial Water Reuse Treatment Systems. If a disinfection process is not part of NSF/ANSI 350-2011 equipment, separate disinfection system equipment is required. The graywater treatment works must be capable of providing a free chlorine residual of 0.2 to 4.0 mg/L in the graywater throughout the indoor graywater plumbing system. The graywater treatment works must include a dye injection system that is capable of providing a dye concentration that is visibly distinct from potable water. |
||
|
Category D graywatera (Non-single family, indoor toilet and urinal flushing) |
Graywater |
The graywater treatment works must be certified under “Class R” or “Class C” of NSF/ANSI 350 Onsite Residential and Commercial Water Reuse Treatment Systems. Required classification shall be dictated by the size of the graywater treatment works and if the graywater sources are residential or commercial as defined by NSF/ANSI 350. Separate disinfection system equipment is required if a disinfection process is not part of NSF/ANSI 350-2011 equipment. A graywater treatment works must be capable of providing a free chlorine residual of 0.2 to 4.0 mg/L in the graywater throughout the indoor graywater plumbing system. The graywater treatment works must include a dye injection system that is capable of providing a dye concentration that is visibly distinct from potable water. |
||
|
Category 1 reclaimed domestic wastewater (evaporative industrial processes, non-construction and road maintenance, non-evaporative industrial processes, restricted access landscape irrigation, non-food crop irrigation and silviculture, non-edible hemp irrigation and zoo operations) |
Domestic wastewater |
E. coli |
<126/100mL monthly geometric mean ≤235/100 mL (single sample maximum) |
Surrogate continuous monitoring required (most parameters)b; E. coli monitoring |
|
Total suspended solids (TSS) |
30 mg/L (daily maximum) |
|||
|
Enteric viruses |
6.0 log reduction |
|||
|
Category 2 reclaimed domestic wastewater (commercial laundries, vehicle washing, washwater applications, oil and gas operations, unrestricted access landscape irrigation, commercial food crop growing operation and non-residential fire protection) |
Domestic wastewater |
E. coli |
<126/100mL monthly geometric mean ≤235/100 mL (single sample maximum) |
Surrogate continuous monitoring required (most parameters)b; E. coli monitoring |
|
Turbidity |
≤3 NTU (monthly average) ≤5 NTU (in more than 5% of results per month) |
|||
|
Enteric viruses |
6.0 log reduction |
|||
|
Parasitic protozoa |
5.0 log reduction |
|||
|
Enteric bacteria |
4.0 log reduction |
|||
|
Category 3 reclaimed domestic wastewater (resident-controlled landscape irrigation, residential fire protection, resident-controlled food crop irrigation, non-commercial food crop growing operation, edible hemp irrigation, toilet and urinal flushing) |
Domestic wastewater |
E. coli |
0 detected in at least 75% of samples (per calendar month) ≤126/100 mL (single sample maximum) |
Surrogate continuous monitoring required (most parameters)b; E. coli monitoring |
|
Turbidity |
≤3 NTU (monthly average) ≤5 NTU (in more than 5% of results per month) |
|||
|
Enteric viruses |
8.5 log reduction |
|||
|
Parasitic protozoa |
7.0 log reduction |
|||
|
Enteric bacteria |
6.0 log reduction |
|||
Sources = 5 Code Colo. Regs. § 1002-84; § 1002-86.
a Category A and C graywater is limited to a design flow of 400 gallons per day or less. Category B graywater is limited to a design flow of 2,000 gallons per day or less. There is no maximum design flow for Category D graywater. The graywater treatment works for Category C and D water must be certified under NSF/ANSI Standard 350. Disinfection (a free chlorine residual of 0.2–4.0 mg/L) and dyeing are required as part of the treatment process.
b Localized reclaimed water treatment systems must be continuously monitored for appropriate process control parameters to demonstrate that systems designed to comply with pathogenic microorganism control are functioning properly. The choice of the type of continuous monitoring technologies to be utilized will be tailored for an individual system and will be included in an operations and monitoring plan. Examples of acceptable forms of continuous monitoring for localized system process control are identified in Table C (5 Code Colo. Regs. § 1002-84).
Upcoming state law or policy
No upcoming onsite non-potable reuse regulations 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 Division (CDPHE WQCC). 2019. Water Reuse in Colorado.
Graywater Control Regulation, 5 Code Colo. Regs. § 1002-86.
Onsite Residential and Commercial Water Reuse Treatment Systems, NSF/ANSI Standard 350.
Reclaimed Water Control Regulation, 5 CCR 1002-84 (2022).
Schoen ME, Ashbolt NJ, Jahne MA, Garland J. 2017. Risk-based enteric pathogen reduction targets for non-potable and direct potable use of roof runoff, stormwater, and greywater. Microb Risk Anal; 5:32-43. doi: 10.1016/j.mran.2017.01.002
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.