Reg. 43 - On-site Wastewater Treatment Systems (OWTS)

two side by side black pipelines embedded in dry earth

The Water Quality Control Commission adopts rules for On-Site Wastewater Treatment Systems (OWTS) called Regulation 43. Once the commission adopts rules, every county health department in Colorado must adopt detailed regulations for small wastewater treatment systems that comply with the commission's rules and the OWTS Act.

The division implements Regulation 43, which governs on-site wastewater treatment or septic systems. Regulation 43 sets minimum standards for how on-site wastewater treatment systems in Colorado (treating 2,000 gallons of wastewater or less per day) should be located, designed, constructed, and used. County health departments use these minimum standards to create local regulations, including permit application requirements, issuing permits, system inspection, and system maintenance.


As part of the regulatory update, the division invites all regulators and practitioners within the onsite wastewater industry and the general public to join the Regulation 43 workgroup and participate in this process.

How to get involved



In Aug. 2023, the division held large group stakeholder meetings to discuss possible changes to the regulation. After we completed our initial walkthrough of the regulation, we identified several topics for further discussion in subgroup meetings. We will hold a final closeout meeting with the large stakeholder group after we conclude the subgroup meetings. The division plans to end all sessions in Aug. 2024, followed by a rulemaking hearing by the commission in spring 2025.

Sign up to receive notifications about this effort.


The Water Quality Control Division has completed its subgroup meetings and is transitioning back to the general stakeholder group to further discuss suggested edits to Regulation 43. The division plans to hold monthly meetings from July through September 2024.

Once the meetings conclude, a copy of the recording, chat, presentation, and other meeting materials will be stored in this public folder.

Scheduled large group stakeholder meetings

After working with stakeholders to review and revise Regulation 43, the division has identified several topics for further discussion in subgroup meetings, including:

  • Leaving soil profile test pits open.
  • P.E. stamp requirements.
  • Mound system design requirements.
  • Transfer of title program requirements.
  • Gradation submission requirements.
  • OWTS sizing reductions for composting toilets.

If you want to join a subgroup, please sign up using this form and select the topics that interest you. We encourage stakeholders to sign up for subgroups related to their professional expertise. The division will share meeting updates with each subgroup list as the schedule is planned. If you want to receive meeting updates regarding a specific subgroup, sign up for that subgroup’s email list.

Scheduled subgroup meetings:

  • Leaving Soil Profile Test Pits Open Subgroup
    • Tuesday, Jan. 9, 2024 | 1 to 3:30 p.m.
    • Tuesday, Feb. 27, 2024 | 1 to 3 p.m.
  • Transfer of Title Program Requirements Subgroup
    • Tuesday, Jan. 16, 2024 | 1 to 3:30 p.m.
    • Tuesday, Feb. 13, 2024 | 1 to 3 p.m.
  • Gradation Submission Requirements Subgroup
    • Tuesday, Jan. 30, 2024 | 1 to 3:30 p.m.
    • Tuesday, March 12, 2024 | 1 to 3 p.m.
  • OWTS Sizing Reductions for Composting Toilets Subgroup
    • Tuesday, April 16, 2024 | 1:30 to 3:30 p.m.
  • P.E. Stamp Requirements Subgroup
    • Tuesday, April 23, 2024 | 1:30 to 3:30 p.m.
  • Mound System Design Requirements Subgroup


For more information, please contact: