Colorado septic rules changed in 2026. Here is what is different.
The state updated its septic regulation and counties have been adopting their own versions. If you are building, replacing or selling, a few things matter to you.
Colorado regulates septic systems through a statewide rule called Regulation 43. The state updated it, and each county then adopts local rules that have to be at least as strict. Counties around Denver have been putting their updated rules in place through 2026.
Most of the changes are technical. A few of them reach a homeowner.
The soil evaluation drives the design
A system has to be sized from an evaluation of the soil on your lot, done by a qualified person. In practice that means test pits dug where the field will go, so the soil layers and any rock or groundwater can be seen.
What it means for you: the soil evaluation is a real, scheduled step that happens before anyone can give you a final design. It is quoted separately from the installation.
Advanced systems come with upkeep
Systems that use a treatment unit get closer oversight than a simple gravity system. Depending on the county, that can mean an operating permit and regular service.
What it means for you: if your lot needs an engineered system, ask what the ongoing requirements are before you build.
Licensing is county by county
Colorado does not have one statewide license for septic installers. Counties license or register the people who work in them, and each county sets its own requirements.
What it means for you: the installer on your job should be licensed for the county where your property sits.
If you are replacing an old system
A system that went in decades ago was permitted under older rules. A replacement has to meet the current ones, which can mean a larger field or a different type of system than what is in the ground now. That is the most common reason a replacement quote surprises people.
If you are selling
Many counties ask for a septic inspection when a home changes hands. See selling a home with a septic system in Colorado.
Check with your county
Rules and fees differ from one county to the next, and they change. Your county public health department has the current version. If you want a price for a system that meets it, call or text (720) 273-0109.