Learning Center · Water
Rainwater Collection in Texas: What Your Roof Can Catch, and What the Law Says
Every roof in Texas is already a rain catchment. This guide uses the Texas Water Development Board’s own manual to explain how much water a roof can collect, which roofing materials are safe for drinking water, the law that keeps an HOA from banning rain barrels, and the state sales tax exemption on the equipment. It is education, not a service we sell.
Updated October 12, 2026
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The short version
- A roof collects about 0.62 gallons per square foot per inch of rain in theory, before losses; a 2,000 square foot roof footprint with the 36.25 inch Austin Camp Mabry normal is about 45,000 gallons.
- Texas Property Code 202.007 bars a homeowners association from prohibiting rain barrels or a rainwater harvesting system, with limits on front yard placement and color.
- Texas Tax Code 151.355 exempts rainwater harvesting equipment and supplies from state sales tax.
- The state manual says asphalt shingle roofs are fine for irrigation water but not for drinking water systems; metal is the preferred catchment.
We do not install rainwater systems. For gutters and the roof that feeds them, start with Get Help or call or text 512-575-5052.
Short version: 2 min. Full page: 7 min. Want the detail? Each section below opens with a tap, or switch to Full at the top to open them all.
Direct Answer
How much rainwater can a Texas roof collect?
About 0.62 gallons per square foot of roof per inch of rain, before losses, according to the state manual.
The rule and a worked example
The state manual gives the number. The Texas Water Development Board’s Texas Manual on Rainwater Harvesting says that in theory about 0.62 gallons per square foot of collection surface per inch of rainfall can be collected, and that in practice some is lost to first flush, evaporation, splash out and leaks. NOAA’s 1991 to 2020 normals put annual rainfall at 36.25 inches at Austin Camp Mabry, the nearest long record station to Round Rock, 37.01 inches at DFW Airport and 51.84 inches at Houston Bush Intercontinental. A 2,000 square foot roof footprint near Round Rock, at 0.62 times 2,000 times 36.25, is about 44,900 gallons a year before losses; the manual puts losses on an asphalt shingle roof at about 10 percent, which brings it to roughly 40,000 gallons.
Measure the footprint, not the slope
Rain falls straight down. The collection area is the roof’s footprint on the ground, not the sloped surface, so a steep roof catches no more than a flat one of the same footprint. Only the part of the roof that drains to the gutters feeding the tank counts.
Catchment
Which roofs are safe to collect from
Metal is preferred, tile and slate work, and asphalt shingle is for irrigation only, per the state manual.
Metal first
Smooth and clean collects best. The manual says the smoother the roof texture the better, names a 55 percent aluminum and 45 percent zinc coated steel sold as Galvalume as a commonly used catchment roofing, and recommends a plain galvanized roof or a metal roof with epoxy or latex paint for drinking water systems. Our roofing materials guide compares metal with the other options for the roof itself.
Asphalt shingle: irrigation, not drinking
Shingles are the common Texas roof, and the manual draws a line. It says composite or asphalt shingles are not appropriate for potable systems because of leaching, but can be used to collect water for irrigation, and it estimates about a 10 percent loss on a composite roof to inefficient flow and evaporation. Clay and concrete tile are porous and can lose about 10 percent too, and slate is called ideal for potable use when no toxic sealant is used.
Watch the metal on the roof
Small parts matter for drinking water. The manual says lead cannot be used as gutter solder on a potable system, because slightly acidic rain can dissolve it, and that copper flashing can discolor fixtures. Older metal gutters are the place to check.
System
Gutters, screens, first flush and the tank
Gutters feed a leaf screen, a first flush diverter dumps the dirtiest water, and the tank stores the rest.
Gutters and downspouts
The gutters are the collector. The manual lists seamless aluminum among the common gutter materials and notes the drop outlet and the elbows that carry water down the wall. Gutters sized and pitched right, with leaf screens, are the same gutters a roof needs anyway; our gutter service covers them, and our edges and drainage guide explains sizing.
First flush
The first water off a roof is the dirtiest. It carries dust, pollen, bird droppings and whatever landed on the roof since the last rain. A first flush diverter routes that water away from the tank. The manual gives a rule of thumb of at least 10 gallons diverted for every 1,000 square feet of roof, more after long dry spells or under trees, and shows a simple standpipe diverter made from PVC pipe.
The tank
Storage is where the money goes. The manual covers tanks from polyethylene to galvanized steel to concrete, and says a tank for drinking water needs a food grade lining and screened openings. Keep the tank dark so algae cannot grow, and keep mosquitoes out with fine screen on every opening.
Texas Property Code
Your HOA cannot ban rain barrels
Property Code 202.007 voids any deed restriction that prohibits rain barrels or a rainwater harvesting system.
What the statute says
The law is direct. Texas Property Code 202.007(a) says a property owners’ association may not include or enforce a provision that prohibits or restricts an owner from installing rain barrels or a rainwater harvesting system, and 202.007(b) says a provision that does is void.
The limits
The same section keeps some say for the association. Under 202.007(d)(6), an HOA does not have to allow a barrel or system on property it owns, on common property, or between the front of the home and the street, and it may object to a barrel in a color that does not match the home or one that displays language or content not typical of a barrel. Side and back yards, in a matching color, are the safe placements. The same chapter, in 202.010, protects solar panels on the roof with its own list of limits.
Texas Tax Code
The sales tax exemption on rainwater equipment
Tax Code 151.355 exempts rainwater harvesting equipment and supplies from state sales tax.
What the statute says
The exemption is in the Tax Code. Section 151.355 exempts from sales tax rainwater harvesting equipment or supplies, water recycling and reuse equipment or supplies, or other equipment, services, or supplies used solely to reduce or eliminate water use. The state manual notes that the buyer claims it with a sales tax exemption form from the Comptroller at the time of purchase; ask the seller for the current form.
Property tax
Property tax relief is local and conditional. The manual explains that a property tax exemption for water conservation equipment goes through a TCEQ use determination and the county appraisal district, and that cities and water utilities may offer their own rebates. Check with your city before you buy a tank.
Common Questions
Questions homeowners ask
How much rain can I collect from my roof in Round Rock?
About 0.62 gallons per square foot of roof footprint per inch of rain, before losses, per the Texas Water Development Board manual. With 36.25 inches a year at Austin Camp Mabry, a 2,000 square foot roof footprint is about 45,000 gallons before losses, and roughly 40,000 after the 10 percent the manual estimates for a shingle roof.
Can I collect rainwater from an asphalt shingle roof?
For irrigation, yes. The state manual says asphalt shingle roofs are not appropriate for drinking water systems because of leaching, and recommends a plain galvanized or painted metal roof for potable use.
Can my HOA stop me from installing rain barrels in Texas?
No. Texas Property Code 202.007 voids any restriction that prohibits rain barrels or a rainwater harvesting system. The HOA can keep them off its own or common property and out of the front yard between the house and the street, can object to a color that does not match the home, and can regulate size, type, shielding and materials where a barrel is visible from a street, another lot or a common area.
Is rainwater harvesting equipment exempt from sales tax in Texas?
State sales tax, yes. Texas Tax Code 151.355 exempts rainwater harvesting equipment or supplies from sales tax. Property tax exemptions are local and go through a TCEQ use determination.
Does The Roof Shepherd install rainwater systems?
No. We install and repair the roof and the gutters that feed one, and this guide is here so you can plan the rest with a rainwater installer.
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