Rain Barrel vs Cistern for Colorado Homes
Both hold roof water. In Colorado, the law often decides which one you can use before taste or budget does.
Most Front Range homes on a city tap stay on the two-barrel rule: up to two rain barrels, 110 gallons combined, outdoor use on the same property, and no Division of Water Resources (DWR) permit. A cistern is a larger-storage conversation — an exempt or small-capacity well, plus a rooftop precipitation collection permit — not a free upgrade under the barrel rule.
This page is about storage and install choices. For the full legal map, see Is Rainwater Harvesting Legal in Colorado? (https://sunhousesystem.com/co-rain-law). Limits below follow the Colorado DWR rainwater page (https://dwr.colorado.gov/services/water-administration/rainwater-storm-water-graywater) and the CSU Extension rainwater guide (https://extension.colostate.edu/resource/rainwater-collection-in-colorado/). It is practical orientation, not a permit or legal advice.
Barrels first for a typical city tap
On municipal water in Denver or Littleton, plan on compliant rain barrels: two sealable, aboveground containers, 110 gallons combined, filled from a rooftop downspout and used outdoors on your property, mainly for lawn and garden irrigation. You may fill and refill them through the year. The cap is how much you store at once, not a seasonal quota.
A buried tank or a large cistern is not that allowance. Calling it a “big rain barrel” does not put it under the two-barrel rule. Larger storage needs the well-based permit route, and only after form GWS-78. If the water system serving the home supplies more than three single-family dwellings, DWR says that larger collection is not allowed under that provision. That is the usual city-tap case. Better storage is legal, sized to the use you are allowed, and installed with care.
What a rain barrel is
Under C.R.S. § 37-96.5-102 (https://colorado.public.law/statutes/crs_37-96.5-102), a rain barrel is a storage container with a sealable lid, sitting aboveground outside the home, collecting from a rooftop downspout. C.R.S. § 37-96.5-103 (https://colorado.public.law/statutes/crs_37-96.5-103), from House Bill 16-1005 (https://leg.colorado.gov/bills/HB16-1005), sets the household limits: no more than two barrels, 110 gallons combined, from a single-family home or a multi-family residence with four or fewer units. DWR treats each home in a duplex, triplex, or townhome as a single-family residence. Drinking and indoor household use are not allowed under this article. There is no DWR permit inside those limits.
Capture under the two-barrel rule is not a water right. The State Engineer may curtail use if a water-right holder shows injury. An HOA may set reasonable appearance and placement rules. It cannot ban barrels that follow the statute.
The irrigation help is real and modest. CSU estimates a full 110 gallons covers about 180 square feet of garden or lawn at about one inch, and that a typical setup fills completely about 10 to 15 times a growing season. Supplemental irrigation still matters for most lawns. Sealable lids also keep mosquitoes out. CSU recommends emptying barrels regularly and disconnecting them if you will be away more than a week. A first-flush diverter is good water-quality practice. The lid is what the law requires.
What a cistern is, and when it belongs
A cistern or tank is larger storage, aboveground or buried, often with a pre-filter or first-flush diverter, a pump, and irrigation controls. That design can fit when the well-based route applies. It is not the default for a Denver or Littleton city tap.
On that route, the residence has, or can qualify for, an exempt or small-capacity well. DWR allows barrels or other water storage structures, with no stated volume cap on roof collection from a building used primarily as the residence. Use is still limited to the well permit. You need the rooftop precipitation collection permit before you collect beyond the barrel allowance. An unregistered well may need form GWS-12 first. See DWR well permitting (https://dwr.colorado.gov/services/well-permitting). We do not issue permits, and we cannot promise approval.
A well permit does not make roof water safe to drink. CSU says untreated roof runoff is not drinking water. Indoor use exists only if the well permit allows it, and it still needs proper treatment.
How to choose
Choose barrels if you are on typical municipal water, you want a modest outdoor assist, and you will manage lids, overflow, and a seasonal drain. Explore a cistern only if you have or may qualify for an exempt or small-capacity well, you are not barred by the “more than three dwellings” rule, and you will talk with DWR about GWS-78 before collecting. Approval is DWR’s decision.
Starting with barrels is sensible on a city tap. Moving past 110 gallons changes the legal route. It is not a hardware swap.
What a designed two-barrel install adds
A professional is not required for legal barrels. Design help still earns a place inside the limit: gutter routing, a first-flush diverter or pre-filter, sealable mosquito-safe storage, an outdoor drip connection, and placement that fits reasonable HOA rules. Overflow should leave the foundation alone.
Sun House System LLC does that two-barrel work through its Rain Harvest Solutions division. For larger storage, design waits until eligibility and the permit path are clear. We do not open a typical municipal consult with a large cistern. Pumps and plumbing ties can also be local building questions, separate from DWR. Check with your department.
Trade-offs without a price tag
Rain barrels (two-barrel rule) — Cistern (well-based route, when eligible)
Typical city-tap home — Usually the legal fit, if compliant — Usually closed when the water system serves more than three dwellings
DWR permit — Not for a compliant 110-gallon setup — Yes — GWS-78 before collecting
Storage — Two containers, 110 gallons combined — No DWR volume cap on that path from the primary residence roof; uses follow the well permit
Complexity — Low to moderate — Higher: design, pump, filtration, siting or burial
Best for — A garden or landscape supplement — Larger outdoor uses, and indoor non-potable uses only if the well permit allows them
Freeze and thaw still means a winter drain. Confirm edge uses such as animals or hot tubs with DWR. This page states no prices. Cost factors and winterizing guides are coming separately.
Ask for a consult that matches your setup
For the two-barrel setup, we help with gutter routing, first-flush or pre-filter, sealable barrels within 110 gallons, and outdoor drip. For larger storage, we discuss a cistern only when an exempt or small-capacity well is in the picture, or when you plan to ask DWR whether one could qualify. Say whether you are on municipal water or a well.
Frequently asked questions
What is the difference between a rain barrel and a cistern?
A rain barrel is a small, aboveground container with a sealable lid, fed by a rooftop downspout. A cistern is larger storage, aboveground or buried, often with filtration and a pump. The two-barrel rule covers compliant barrels. Larger structures generally need the well-based permit.
Can a typical Denver or Littleton home install a cistern?
Not under the rain-barrel statute. If a municipal or shared system serves more than three single-family dwellings, that larger collection is not allowed under that provision. Plan on two barrels unless DWR says otherwise.
Do I need a permit?
Compliant two-barrel setups (≤110 gallons combined) do not need a DWR permit. A cistern on the well-based route needs GWS-78 before you collect. A buried tank is not a rain barrel under the statute.
Can I start with barrels and add a cistern later?
You can start with compliant barrels. Larger storage needs well eligibility and a permit before you collect on that route. It is not an automatic upgrade.
Can I drink barrel or cistern water?
Not under the two-barrel rule. The statute bars drinking and indoor household use, and CSU says untreated roof runoff is not safe to drink. On the well-based route, indoor uses — if any — follow the well permit and still need proper treatment.
Sources
- Colorado DWR rainwater page (https://dwr.colorado.gov/services/water-administration/rainwater-storm-water-graywater)
- CSU Extension rainwater guide (https://extension.colostate.edu/resource/rainwater-collection-in-colorado/)
- C.R.S. § 37-96.5-103 (https://colorado.public.law/statutes/crs_37-96.5-103)
- C.R.S. § 37-96.5-102 (https://colorado.public.law/statutes/crs_37-96.5-102)
- House Bill 16-1005 (https://leg.colorado.gov/bills/HB16-1005)
- DWR well permitting (https://dwr.colorado.gov/services/well-permitting)
Sun House System LLC, Rain Harvest Solutions division. We are not DWR. Confirm with DWR before storing more than the barrel allowance.