In this guide
There is a thing people repeat about rainwater that is not true, and it is worth clearing up in the first paragraph: rainwater harvesting is not illegal in Colorado. It has not been since 2016. The internet still says otherwise on a lot of pages, including pages that were written after the law changed.
What is true is that rainwater is regulated unevenly, that the regulation has almost nothing to do with environmental policy and almost everything to do with water-rights law in the West, and that the rules change at the state line. A system that is unremarkable in Texas needs a licensed engineer's design in Arkansas.
So here is the state-by-state version, the arithmetic for how much water a roof actually produces, and the parts that go wrong.
Why rainwater is regulated at all
In the eastern states it mostly is not, and the rules you run into are plumbing code rules about keeping nonpotable water out of the drinking supply. In the West it is a water-rights question, and that is a different animal.
Western water runs on prior appropriation, which treats water as a public resource already spoken for by whoever claimed it first. Under that logic, precipitation that would have run off your roof into a ditch and down to a senior water right is water you are intercepting out of priority. Colorado's own legislature wrote that reasoning into the rain barrel bill, declaring that nothing in it infringes on prior appropriation and that using a rain barrel does not create a water right.
Whether that logic survives contact with reality is a separate argument. Colorado's legislature required the State Engineer to report on whether rain barrels had caused any discernible injury to downstream water rights. What matters for you is that it explains why the map looks the way it does.
The ten states, specifically
| State | Rooftop collection | Potable use | What to watch |
|---|---|---|---|
| Arizona | No restriction, no permit | Not addressed at state level | A state tax credit is often cited and appears to have expired |
| Arkansas | Allowed | Statute addresses nonpotable only | A plumbed system requires a licensed engineer's design |
| Colorado | 110 gallons in two barrels, or a permit for more | No, outdoor use only | The permit path is tied to an exempt well and is widely unknown |
| Florida | No restriction | Plumbing code sets nonpotable standards | Collection from parking or walking surfaces is largely prohibited |
| Minnesota | No restriction | Code covers nonpotable only | A plumbed system must be designed by a registered engineer |
| Nevada | Rooftop of a single-family dwelling only | No, nonpotable only | Ground catchment is not covered by the exemption |
| New Mexico | Allowed and encouraged | Not restricted | Contact the State Engineer before building anything large |
| North Carolina | No restriction | Local plumbing authority decides | Potable storage needs cistern materials rated for it |
| Oregon | Roof surfaces exempt from water rights | Yes, with a permit and a licensed design | Ground catchment is not exempt; tanks over 5,000 gallons need a building permit |
| Texas | No restriction, three tax incentives | Yes, with licensed installation | Backflow rules apply if a public supply feeds the tank |
Colorado deserves the longer answer because it is the one everybody gets wrong. The no-permit path, created in 2016, allows no more than two rain barrels holding 110 gallons combined, collected from the roof of a building used primarily as a residence, used outdoors on the same property. The statute specifically bars drinking water and indoor household use, and the State Engineer can curtail use during a shortage.
The second path is older and larger and almost nobody mentions it. Under the 2009 legislation, a residence that has or could qualify for an exempt well permit can apply to the Division of Water Resources for a rooftop precipitation collection permit. The Division's own guidance says there is no limit on the amount you can collect from the roof of a building used primarily as your residence, and uses may include indoor uses to the extent the underlying well permit allows. You need the permit before you start collecting, but the ceiling is not 110 gallons.
Nevada went the other direction and kept it narrow. The 2017 statute puts de minimis collection outside the water-rights chapter entirely, with no permit and no water right needed, but only for collection from the rooftop of a single-family dwelling and only for nonpotable domestic use. Ground catchment, berms and swales are not covered.
Oregon's exemption is for precipitation collected from an artificial impervious surface. Oregon State University Extension reads that as applying only where the water never touches soil between the roof and the tank, which means ground catchment needs a water right. Oregon is also the clearest state in our ten on drinking it: potable rainwater systems are allowed, require a plumbing permit, and must be designed by a licensed professional under the plumbing code's own appendix.
How much water you actually get
The arithmetic is simple and it is where most articles mislead. One inch of rain on one square foot of roof is 0.623 gallons. That is pure unit conversion: an inch over a square foot is 144 cubic inches, a US gallon is 231 cubic inches, and 144 divided by 231 is 0.6234. There is no efficiency in that number at all.
Real systems lose water to first-flush diversion, splash, evaporation and leaks. The Texas Water Development Board puts real-world system efficiency at 75 to 90 percent and uses 80 percent in its own public-facing rule of thumb, which comes out to roughly 1,000 gallons for every inch of rain on a 2,000 square foot roof. That is half a gallon per square foot per inch after losses, and that is the number to plan with.
Roof material matters to the loss rate as well as to the water quality. Composition and asphalt shingle costs you around 10 percent, clay and concrete tile up to 10 percent, and smooth metal is the best catchment surface there is.
Run the numbers for your own parcel before you buy a tank. A 1,200 square foot roof in a county that gets 14 inches a year collects roughly 8,375 gallons across the whole year at 80 percent efficiency, which averages about 23 gallons a day. That is a useful supplement. In the arid West it is not a household water supply, and anybody telling you otherwise has not done the multiplication.
What goes wrong
First flush is the one everyone knows about and the one people still skip. The initial runoff carries whatever has been sitting on the roof since the last rain: dust, pollen, bird and rodent droppings, leaf litter. The Texas manual's sizing rule is a minimum of 10 gallons of diversion for every 1,000 square feet of collection surface, with cited research suggesting considerably more. Virginia's state specification puts it as diverting the first 0.02 to 0.06 inches of rooftop runoff.
Roof chemistry is the one people do not know about, and the numbers are stark. Washington's Department of Ecology ran a controlled study of roofing panels across 20 rain events and measured median concentrations in the runoff. Treated wood shakes gave up arsenic at 1,385 micrograms per liter and copper at 825. Copper panels released copper at 1,905. Asphalt shingles were low on metals generally, but shingles with algae-resistant copper granules still put copper into the water. Painted galvanized steel and EPDM were among the cleanest.
Which translates to a short rule: smooth metal good, treated wood shakes never, copper never, asphalt shingle acceptable for irrigation and questionable for anything you drink. Lead cannot be used as gutter solder, because slightly acidic rain will dissolve it.
Microbial load is why nobody should drink unfiltered cistern water. A North Carolina State review of rooftop runoff found fecal coliform between 144 and 1,117 colonies per 100 millilitres, against a drinking water standard of zero. CDC puts it plainly: rainwater is not necessarily safe to drink without first removing germs and chemicals. Where extension sources describe a potable treatment train, it is filtration down to around half a micron combined with ultraviolet disinfection.
Mosquitoes are a code issue as much as a nuisance one. CDC's guidance is a screen where water enters the system, or emptying an open barrel at least every ten days. North Carolina State specifies mesh of one millimetre or smaller over any open water pathway.
Freezing is the failure mode people in Colorado, Minnesota, northern Nevada and the Oregon high desert underestimate. Virginia's state specification gives three options for cold climates: put the tank underground or indoors, disconnect and drain it for winter and accept that you have no system from November to March, or heat-tape the exposed piping and run year round. Pick one deliberately rather than discovering it in January.
And the structure has to hold. Water weighs 8.34 pounds a gallon, so a full 2,500 gallon tank is about 20,800 pounds sitting on whatever you set it on. Oregon requires a building permit for tanks over 5,000 gallons, which tells you how seriously the engineering is taken.
What it costs
EPA's literature review is the best cited source on this and it is blunt. A typical 50-gallon plastic rain barrel with a spigot and overflow runs around $70. Cistern storage runs $1.50 to $3.00 per gallon of capacity, with the per-gallon cost dropping as tanks get bigger. Pumps, controls, filtration and treatment add another $2 to $5 per gallon of system capacity.
EPA also runs the payback math and does not flatter the result: a 3,200 gallon cistern sized for a one-inch storm on a 5,000 square foot roof carries a life-cycle cost of about $31,000, and against typical US water prices that system would need to fill and fully draw down more than 3,800 times to pay for itself. That calculation is for someone who already has a water bill.
For a rural parcel with no water service the comparison is completely different, and that is the real case for catchment. You are not competing with municipal water at $2.50 per thousand gallons. You are competing against hauling water in a tank on a trailer, or against a well that may cost five figures and may come up dry. At that scale a large tank and a good roof look much better.
Texas is worth a note here because the incentives are real: state sales tax is exempt on rainwater harvesting equipment and installation, there is a local-option property tax exemption for water conservation, and state law voids HOA bans on rain barrels.
Covenants, which are not the same as state law
Of our ten states, only Texas and Colorado have a confirmed statute voiding covenant restrictions on rainwater collection. Texas property code bars a dedicatory instrument from prohibiting rain barrels or a rainwater harvesting system, while letting the association regulate placement in the front yard, color consistency and shielding where the system is visible from a street. Colorado's rain barrel act amended the common interest ownership act so an association cannot prohibit compliant rain barrel use, though it may impose reasonable aesthetic requirements.
Everywhere else, the covenants and the subdivision's bill of assurance control, and we could not find a statute protecting you. Arizona in particular is often reported as having HOA protection for rainwater and we could not verify it: the bill that would have created it appears never to have passed, and the statute people cite covers solar energy devices. If you are buying in a platted subdivision, read the covenants.
The order to do this in
The order to do this in
Find out what your state allows before you price anything.
The table above is the starting point. Colorado and Nevada are the two where the answer actually constrains the design.
Pull the monthly rainfall normals for the nearest station.
Not the annual total. You are sizing for the longest dry run, and the monthly distribution is what tells you how long that is.
Measure the roof footprint, not the sloped surface.
Plan area is what collects rain. Multiply by inches, by 0.623, by 0.8 for a realistic annual yield.
Decide potable or not, and decide it now.
It changes the roof material, the piping, the permit, and in several states who is allowed to design the system. Retrofitting from nonpotable to potable is expensive.
Put in a first-flush diverter and a screen on day one.
At least 10 gallons of diversion per 1,000 square feet of roof, and mesh of one millimetre or smaller anywhere water can get in.
Plan for freezing if you are anywhere cold.
Underground, drained seasonally, or heat-taped. Those are the three choices and doing nothing is not one of them.
Where this fits for a Landopia buyer
Catchment is a good supplement on nearly any rural parcel and a genuine primary supply only where rainfall and roof area are both generous. In the arid West it buys you garden water, livestock water and a buffer, not a household supply. In Florida, Arkansas, Minnesota and North Carolina the arithmetic is much friendlier.
Either way it does not stand alone. The approval that decides whether you can occupy a dwelling is the sewage approval, and the water supply question is tangled up with well permits that vary by state and sometimes by basin. We went through all of that in the guide to living off the grid, and if you want to know whether your ground will even take a system, that starts with what a soil test actually tells you.
If you are shopping for ground where this kind of setup makes sense, start with our off-grid land listings and check the county rainfall before you check the view.
Catchment is one of the few parts of rural self-sufficiency where the engineering is genuinely simple and the arithmetic is genuinely honest. Roof area times rainfall times 0.8. There is no way to argue with it and no salesperson can talk it up.
Which is why it is worth doing the multiplication before you fall for a tank. The ground and the sky over it will tell you what is possible, and then you build to that.
