How much water can I collect from my roof?

A common rule of thumb is about 600 gallons per inch of rain per 1,000 square feet of roof. Even small storms fill a rain barrel quickly.

Can my HOA stop me from using rain barrels?

It depends on your state. In Texas, Property Code § 202.007 generally prevents HOAs from prohibiting rain barrels, though they can regulate appearance. Check your state’s rules.

Are rain barrels legal in Colorado?

Yes, within limits. Since 2016, single-family homes can use up to two barrels with a combined 110 gallons for outdoor use.

What happens when the barrel is full?

Water must overflow somewhere. Use a diverter or an overflow hose that sends excess water well away from the foundation.

Rainwater Harvesting From Your Gutters

Rainwater harvesting from your gutters

Your gutters already collect every drop that falls on the roof. With a barrel or tank, some of that water can go to the garden instead of the storm drain. Here is how rainwater harvesting works, what the rules are in different places, and how to set it up without creating water problems at the house.

By Local Gutter Network · Updated September 30, 2026

How much water a roof collects

A roof collects more water than most people expect. A common rule of thumb in rainwater harvesting guidance, including from Texas A&M AgriLife, is that one inch of rain on 1,000 square feet of roof yields roughly 600 gallons. A single summer storm can fill a 55-gallon barrel many times over. That is why every rainwater setup needs a plan for overflow.

The parts of a system

Gutters and downspouts (conveyance): they bring the water to the storage. Texas A&M AgriLife’s rainwater harvesting guidance covers how gutters and downspouts should be sized and kept clean for collection.
Screens or guards to keep leaves out.
First-flush diverter: a device that sends the first, dirtiest water from each storm (roof dust, pollen, bird droppings) away before the rest enters the tank.
Storage: a barrel (often 55 gallons) or a larger tank or cistern.
Overflow: an outlet that sends excess water away from the foundation when storage is full.
Outlet: a spigot or pump for using the water.

Barrels vs. tanks

Rain barrels are inexpensive and easy: a 55-gallon barrel under a downspout diverter supplies water for a garden bed or containers. They fill quickly and are best for small uses. Tanks and cisterns, from a few hundred to several thousand gallons, store enough to water a yard through dry spells and need a pad, proper overflow and often a pump. Larger systems benefit from gutters and downspouts planned around them from the start.

Rules differ a lot by state and city

Texas: Texas Property Code § 202.007 generally prevents property owners’ associations from prohibiting rain barrels and rainwater harvesting systems, although they can regulate size, type and appearance in visible locations. See San Antonio and Austin.
Austin: Austin Water has offered a capacity-based rebate of $0.50 per gallon for non-pressurized and $1.00 per gallon for pressurized systems, up to $5,000 per site and 50% of system cost, with pre-approval for tanks over 500 gallons.
Colorado: since 2016, state law (HB16-1005) allows single-family homes and buildings with up to four units to use up to two rain barrels with a combined 110 gallons for outdoor use. See Denver.
Washington, DC: DOEE’s RiverSmart Homes program has offered rain barrels with a co-payment after a stormwater audit. See Washington, DC.
Philadelphia: the Water Department’s Rain Check program has offered free rain barrels to city residents after a workshop. See Philadelphia.
Chicago area: the MWRD has distributed rain barrels to Cook County residents who disconnect downspouts from the sewer. See Chicago.

Program terms change; check current rules before you buy. Some places also have rules about using harvested water indoors; most homeowner systems are for outdoor use only.

Setting it up without water problems

Choose the downspout. Pick one that drains a good section of roof, near where you will use the water, on level, stable ground.
Raise the barrel on a solid base so a hose or watering can fits under the spigot. A full 55-gallon barrel weighs well over 400 pounds, so the base must be firm.
Install a diverter or first-flush device so the downspout still works normally when the barrel is full.
Route the overflow at least several feet from the foundation onto ground that slopes away, or into a rain garden.
Screen all openings to keep out mosquitoes and debris.
Winterize in cold climates: drain and disconnect barrels before freezing weather, and restore the normal downspout path.

Sizing storage to your needs

Match the storage to how you will use the water. A few 55-gallon barrels cover containers, vegetable beds and shrubs between rains in many climates. Watering a lawn takes much more: a rule of thumb for lawn irrigation is roughly 0.6 gallons per square foot per inch of water, so a 1,000-square-foot lawn needs about 600 gallons to receive one inch. That is why lawn irrigation from rainwater usually requires tanks rather than barrels.

Climate matters too. Where rain falls regularly all year, smaller storage refills often. Where long dry spells follow a rainy season, as in much of Texas and the West, larger tanks are needed to carry water through the dry months. Several barrels can be linked together so they fill in sequence.

Water quality and safe use

Rainwater from a roof is not drinking water. It can carry dust, pollen, bird droppings, and material from roofing and gutters. For garden use, most homeowners simply avoid spraying it on the edible parts of vegetables shortly before harvest and water the soil instead. Treating rainwater for drinking or indoor use is a different project that requires filtration, disinfection and, in many places, permits.

Roof material also affects water quality. Metal and many modern shingles are common collection surfaces; treated wood shakes are generally not recommended. Ask the gutter installer about materials if you plan to collect water. See gutters for metal roofs.

Mosquitoes and maintenance

Standing water attracts mosquitoes. Fine mesh screens on every opening, a tight lid, and emptying the barrel regularly in summer prevent breeding. Check screens, diverters and hoses a few times a year, and clean out sediment from the bottom of barrels and tanks at least once a year.

Keep the gutters clean

The quality of collected water depends on the roof and gutters. Guards or regular cleaning keep leaves and needles out of the storage, and a first-flush diverter helps with fine dirt. Gutters that stay clear also deliver more water to the barrel instead of overflowing at the front. See are gutter guards worth it?

Planning gutters around a tank

If you plan a larger system, tell the gutter installer before the work starts. Downspouts can be moved or added so that several roof sections feed the tank, and larger 3x4-inch downspouts deliver water with fewer clogs. Leaving a clean path from the gutter outlet to the tank inlet also makes maintenance easier. See downspout size and placement.