Rainwater collection: setup, treatment, and your state's rules
Rainwater collection is legal in all 50 states, a basic setup costs $60 to $200, and one inch of rain on a standard residential roof produces enough runoff to fill a 55-gallon barrel in a single event. The conversation has moved past legality — the practical questions now are what to buy, how to install it, and what to do with the water before you drink it.
State rules in brief
Forty-seven states: no restrictions on residential rainwater collection. Colorado caps household collection at 110 gallons from a residential rooftop — two standard 55-gallon barrels — for use on the same property. Utah permits up to 2,500 gallons with a free online registration through the Division of Water Rights. Nevada requires permits for larger systems; barrel-scale collection is generally unrestricted.
Many states offer rebates through local water utilities. Before purchasing anything, search for "[your city/county] rain barrel rebate" — a $30 to $80 rebate on a $80 to $120 barrel is common enough that checking takes less time than the rebate is worth. Texas, Florida, North Carolina, and Virginia have the most active rebate programs, but meaningful programs exist in dozens of municipalities.
The basic setup: what you need
The barrel — $50 to $120
A 50 to 55-gallon food-grade or UV-stabilized polyethylene barrel with an overflow outlet, a spigot near the base, and a screened inlet to keep debris and mosquitoes out. RTS Home Accents and FCMP Raincatcher 4000 are the two most available models at major retailers. Flat-back designs fit flush against a house wall. Avoid barrels without screens — standing water without screening breeds mosquitoes in three to five days.
A downspout diverter — $20 to $40
A diverter installs inline on the downspout and routes water into the barrel through a flexible hose. When the barrel is full, the diverter automatically redirects overflow back down the downspout — preventing barrel overflow at the foundation. Do not simply cut the downspout short and place a barrel underneath; this leads to foundation drainage problems when the barrel is full.
A first-flush diverter — $20 to $50, strongly recommended
The first water that runs off a roof after a dry period carries concentrated bird droppings, atmospheric particulates, roofing material residue, and debris. A first-flush diverter captures and discards this initial flow — typically the first gallon — before cleaner water enters the barrel. Not strictly required for garden irrigation use, but meaningful if the water might contact edible plants or be treated for emergency drinking use.
A raised platform — optional but useful
The spigot on a rain barrel works by gravity. A barrel at ground level delivers water slowly. Raising the barrel 12 to 18 inches on a stable platform — cinder blocks, a purpose-built stand — provides enough head pressure to fill a watering can or bucket at a useful flow rate and allows access for containers placed under the spigot.
What collected rainwater is appropriate for
Roof-collected rainwater is appropriate for outdoor irrigation, garden watering, washing tools and equipment, and non-contact uses. Use it freely for these purposes — it is what most rain barrel installations are primarily for, and it is what most utility rebate programs specifically support.
For emergency drinking use, roof-collected rainwater requires treatment. Even with a first-flush diverter, rainwater carries biological contaminants from bird droppings and atmospheric particulates, and may carry chemical contamination from roofing materials, gutters, and atmospheric deposition depending on your location. The treatment sequence for emergency drinking use:
- 1.Pre-filter through a fine mesh or coffee filter to remove particulates
- 2.Filter through a Sawyer Squeeze or similar 0.1-micron hollow fiber filter to remove bacteria and protozoa
- 3.Disinfect with purification tablets or boiling to address viruses not removed by the hollow fiber filter
A certified gravity filter with pathogen removal claims — ProOne Big+ or British Berkefeld — can handle both filtration and disinfection in one step for biological contaminants. Chemical contamination from roofing materials is a separate consideration that a portable filter does not address; treat roof-collected water as an emergency supplement, not a primary drinking source.
Winterizing
Before the first hard frost in your area, drain the barrel completely, disconnect the diverter hose, and cap or remove the downspout diverter. Store the barrel indoors, in a garage, or inverted outside to prevent water from collecting and freezing inside it. A full barrel freezes solid and can crack the polyethylene. This takes fifteen minutes and saves you a barrel next spring.
What to do right now
- 1 Check for a local rebate before buying anything. Search "[your city] rain barrel rebate" — a rebate reduces the cost to near zero in many jurisdictions.
- 2 Pick a downspout location with adequate roof catchment area. A downspout draining 300 to 600 square feet of roof fills a 55-gallon barrel from a single inch of rain — typical of most residential downspout zones.
- 3 Add a first-flush diverter if the water might contact edible plants or be used for emergency drinking. For general irrigation only, a standard screened barrel without first-flush is sufficient.
- 4 Mark your calendar for winterization. The barrel needs to be drained and stored before the first hard freeze in your area. Set a reminder for October or November depending on your climate.
On the shelf
Rain Barrel — 50 to 55 Gallon
RTS Home Accents and FCMP Raincatcher 4000 are the two most available models at major retail. Both are UV-stabilized polyethylene with screened inlets and flat-back designs. Check local rebate programs before purchasing.
Full rain barrel comparison →Go deeper
Full guidance on NWS:
Related field notes
Sources
- EPA: Soak Up the Rain — Rain Barrels
- Colorado Division of Water Resources: Rainwater Harvesting Rules
- Utah Division of Water Rights: Rainwater Harvesting Registration
- Penn State Extension: Rainwater Harvesting — Treatment and Use