A guest house on a Nathrop property needs two separate approvals, and they look at it differently. Chaffee County looks at the floor area, the zoning, and how the lot was created. The Colorado Division of Water Resources looks at the kitchen and what the well permit already says. A listing can pass the county's test and still fail the state's. A buyer who doesn't know that can end up owning a cabin with nowhere legal to plug in a stove.
What the county allows on a rural parcel
Chaffee County adopted its new Land Use Code on November 19, 2024. It took effect January 1, 2025, and the posted version was amended September 16, 2025. The county's October 6, 2026 Board of County Commissioners and Planning Commission agendas did not list any ADU change.
Under the current code, an accessory dwelling unit next to a single-family home has to be detached from the main house. In the Agriculture/Ranching (AR) and Residential Rural (RR) zones, an ADU can be no larger than 1,500 square feet or the main building's floor area, whichever is smaller. Most properties get one ADU. A second one is possible only when the main house and both ADUs connect to public water and sewer, which rules it out on most well-and-septic acreage.
One provision matters a lot around Nathrop, where older cabins sit on land people want to build on. Under the code's "principal conversion" rule, an existing home can be re-designated as the accessory unit to a new main house, as long as both buildings meet the code. So on paper, you can build new and keep the old cabin.
The county also hands the water question to someone else. The applicant has to show that adequate water and wastewater service is available for the ADU when applying for the building permit, under Colorado Department of Public Health and Environment, Colorado Division of Water Resources, and county septic standards. The county's yes depends on the state's answer about the well.
When the parcel was created changes the count
The code counts ADUs against a zone's density in a way that depends on the lot's history. RR allows one unit per 5 acres in general, and AR allows one per 35 acres. An ADU on a well and septic system counts as half a dwelling unit. It counts as zero if it connects to a public water system, or if it is built on an AR or RR lot of record created before January 1, 2025.
So two Nathrop parcels with the same acreage, the same well, and the same view can count the same guest house differently because one was platted in 2019 and the other in 2025. The difference shows up mostly when density gets tested, such as a later lot split. The county applies its density and open-space standards to any subdivision that creates a net new residential lot. The streamlined minor subdivision process can be used only once on a given property. A listing description won't tell you when the lot was created. The plat will.
The stove test
The state uses a different line, and it is drawn in the kitchen. Division of Water Resources Guideline 2016-1, amended December 20, 2023, decides whether a detached living space is part of the main house or a separate single-family dwelling. A well permitted for one dwelling can serve both buildings with no permit change only if the auxiliary space meets every one of these conditions:
- It is not rented, leased, or occupied by anyone other than a guest, a family member, or a caregiver or employee who would otherwise live in the main house.
- It does not use water for business or public purposes.
- If it has its own entrance, it has no kitchen facilities.
The guideline treats a space as having kitchen facilities if it has a stove or oven, a 240-volt cooking hookup or equivalent gas piping, or a refrigerator over 6 cubic feet. In the guideline's words, "A wet bar with a sink and a refrigerator no more than 6 cubic feet in size is acceptable." If the space fails any of the conditions, the well permit has to cover two or more dwellings.
The guideline also covers county definitions. If a county's definition of an ADU requires kitchen facilities, DWR treats every ADU in that county as a separate dwelling, whatever the owner plans to do with it. Chaffee County's code defines a dwelling unit as a space with "permanent provisions for living, sleeping, eating, cooking, and sanitation." Taken together, these rules suggest a building permitted as an ADU in Chaffee County will usually be treated as a second dwelling for well purposes. A bunkhouse or studio without a kitchen, used by family and guests, falls under a different set of rules. For a specific property, that is a question for DWR and the county.
Acreage and well age decide what the permit can do
Once a structure counts as a second dwelling, the next question is whether the existing well permit can cover it. Under DWR's guideline, the answer depends on parcel size and the well's history.
| Situation | What DWR's guideline describes |
|---|---|
| Only well on a 35+ acre parcel, permitted under C.R.S. 37-92-602(3)(b)(II)(A) | Household use inside up to three single-family dwellings; if the permit doesn't specify a number, it may be amendable to three |
| Well on a parcel under 35 acres, permitted for one dwelling | Typically re-permitted for two dwellings only under a decreed augmentation plan |
| Domestic well first used before May 8, 1972, historically serving one dwelling | Typically expanded to two dwellings only under a decreed augmentation plan |
DWR's separate Guideline 2023-1 adds that the ordinary exempt permit for a non-cluster parcel under 35 acres covers household use inside one dwelling, with no outdoor use. Many Nathrop-area acreage parcels are under 35 acres, so the guest house question often comes down to augmentation. Even on large parcels, the permit's wording matters more than the acreage. Parcel size alone doesn't authorize three dwellings. The permit's conditions do.
Why augmentation exists, and what it costs
Greg Felt, general manager of the Upper Arkansas Water Conservancy District, explained the reason in a May 7, 2026 Ark Valley Voice article. "We are in an over-appropriated river basin," Felt said, "Meaning there are more rights than there is water to satisfy the rights." He added that a compact with Kansas limits net consumptive use in Colorado's Arkansas Basin to 1948 levels. Well owners pay for the water they consume, not the amount they pump, and the district replaces that consumed water so senior rights holders aren't harmed.
The district runs a blanket augmentation plan. It sells replacement water that people can use to drill a new well or expand the use of an existing one. The plan covers areas inside its "Blue Line" boundary, which the district describes as covering most of Chaffee County and western Fremont County. The district asks property owners to contact its office to confirm whether a specific parcel is inside.
The posted standard fees are for one unit, which is 0.10 acre-feet and covers household use plus about 1,400 square feet of lawn or garden:
- Augmentation application fee: $200, once per application
- Augmentation fee: $3,850 per unit, one time
- Annual storage and maintenance fee: $165 per unit
- DWR new well permit fee: $100
The district lists the total as $4,315 and notes that prices can change. Because the $100 state fee is labeled as a new-well-permit fee, the total may not match the cost of amending an existing permit.
Augmentation also comes with ongoing requirements. The district's application form, revised February 3, 2025, requires a totalizing meter and annual reporting, with the $165-per-unit payment due by March 15. Pumping above the allotment is charged at $0.005 per excess gallon, with a $50 minimum. The same form says unused augmentation water can't be carried over to the next year. An undated district brochure estimates about 100 days to process and approve the well permit after purchase, so timelines are worth confirming directly.
What to check before writing an offer
All of the above affects what a buyer should ask for while the contract is still open. Before you count a cabin, studio, or guest house as part of the property's value, look at these:
- The well permit itself. Get the permit number and read its conditions, especially how many dwellings it covers and whether outdoor use is allowed.
- Parcel acreage and creation date. Is it 35 acres or more, and was the lot of record created before January 1, 2025? The answers affect both the state's permit options and the county's density count.
- The existing structure's kitchen. Check for a range, a 240-volt or gas cooking hookup, or a full-size refrigerator in a detached building with its own entrance.
- Augmentation on record. If the seller already bought augmentation, the district has a transfer form for the new owner, which the district notes the title company usually handles at closing.
- Blue Line status. If augmentation would be needed and none is on record, confirm with the district that the parcel is inside its service boundary.
None of these questions has the same answer on every Nathrop parcel. The county code, the state guideline, and the well permit together decide what a guest house can legally be. The building permit file and the district office are the places to confirm it for a specific property.
If you're looking at Nathrop acreage with a cabin you'd like to keep, or a lot where you hope to add a guest house later, Mary Kale can help you get the well permit, plat, and augmentation records in front of you before you commit, so you know which rules apply to that parcel. Contact Mary Kale to start that review.
This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.
