On Nov. 14, 2022, the Colorado Water Quality Control Commission (WQCC) adopted new regulations to authorize and guide water suppliers in implementing Direct Potable Reuse (DPR). DPR is the process of directly connecting fully treated wastewater effluent into a potable water supply system without first discharging it into an environmental buffer, such as a lake or stream, for further treatment and distribution as finished drinking water. While various municipalities across the country have selectively used DPR, before now it has not been approved for statewide use in Colorado. With the WQCC’s adoption of the new DPR rule in Regulation 11, the path is now clear for municipal water suppliers in Colorado to take advantage of this process that presumably would reduce the expense and burden of acquiring new water supplies.

Utilities have traditionally discharged treated wastewater effluent into environmental buffers, including surface water bodies or groundwater. While doing so can present some benefits, such as dilution or natural attenuation of pathogenic and chemical contaminants, it can also present disadvantages in arid environments like Colorado due to significant water losses from evaporation, seepage or evapotranspiration. The benefits of environmental buffers are also diminished based on advancements in water treatment processes; treated wastewater effluent no longer needs to be blended with environmental buffer water before being processed at drinking water treatment facilities. Additionally, the use of environmental buffers often increases utilities’ capital and operations costs due to the need for storage, injection, recapture and/or conveyance infrastructure. Expanded reuse has long been a goal in Colorado and its importance has only grown due to the anticipated gap between available water supplies and demands, as recognized by the Colorado Water Conservation Board’s (CWCB’s) 2015 Colorado Water Plan and the Draft 2023 Water Plan Update. In fact, the Draft 2023 Water Plan Update expressly included as a goal the strategic expansion of water reuse and development of a water reuse progress report for greater visibility.

Although no state or federal law has prevented the implementation of DPR, a primary challenge has been public opinion, with hesitation about imbibing drinking water that started out as wastewater effluent. Thus, while the WQCC sees the practice of DPR as inevitable and many water suppliers were already exploring DPR solutions, misperceptions regarding the safety of DPR could critically undermine DPR. To combat this, the new regulations ensure uniform monitoring, reporting and public communication requirements—some specifically tailored to protect members of disproportionately impacted communities. These requirements supplement past and future projects aimed to expand public awareness of DPR safety and benefits. For example, with grant funding from the CWCB, Colorado Springs Utilities and the Colorado School of Mines developed a mobile demonstration project to educate communities on DPR and allow them to see and taste the treated potable water (in some cases, by supplying several breweries with treated water).

The DPR rule requires water suppliers hoping to implement DPR programs to gain approval from the Colorado Department of Public Health and Environment first. Prior to being approved, applicants will undergo a technical, managerial and financial assessment, in addition to supplying one year of test results on treated wastewater. Each system must be equipped with several “critical control points” that are capable of automatically shutting down when exceedances on target chemicals and pathogens are detected. The integrity of these control points will be monitored regularly to ensure DPR programs are operating at the highest level of safety. Among other requirements, the DPR rule requires suppliers to:

  • Develop and maintain a written enhanced source water control program demonstrating how the supplier will reduce, eliminate or alter the nature of constituents of concern in treated wastewater.
  • Develop and maintain a DPR operations program demonstrating how the supplier or wastewater entity will operate wastewater treatment processes and DPR.
  • Perform regular monitoring at critical control points for several target chemicals and indicator compounds, which may include unregulated chemicals such as per- and polyfluoroalkyl substances (PFAS).
  • Utilize a minimum of three separate critical control points for pathogen reduction, two of which must consist of one disinfection control point utilizing UV or ozone, and one filtration control point consisting of reverse osmosis, conventional or direct filtration, or an alternative filtration.

As Colorado’s hydrological environment changes, some water suppliers are concerned that depleted groundwater supplies once used as an environmental buffer could trigger the DPR rule’s heightened testing requirements if injection and withdrawal are deemed to be too close. The WQCC clarified that so long as a water supplier could show that discharged wastewater took more than 50 days to travel through a purifying aquifer, regulations related to the Groundwater Under the Direct Influence (GWUDI) Policy, and not the DPR rule, would apply. The WQCC conceded that in practice, water suppliers using Indirect Potable Reuse (IPR) through environmental buffers may still need to increase water quality monitoring to show that the DPR rule does not apply to their water supplies.

While approval of the DPR regulations is a critical step toward meeting Colorado’s future water needs, implementation will require both years of preparation and significant investments of resources that many water suppliers may not be prepared to make immediately. Entities considering undertaking a DPR project (or those concerned that an IPR-based system might become subject to the DPR rule) should closely review their operations and facilities to ensure compliance with applicable regulations. Any modifications to how water supply systems operate may impact water rights and their administration, and entities should undertake a close review of anticipated impacts. Additionally, given the significant investments required for DPR, utilities considering such projects should evaluate funding opportunities and initiate early engagement with policymakers and stakeholders.