Rainwater Harvesting

In Central Texas, if you have a roof area of 2,500 square feet and a yearly average rainfall of 32 inches, you can collect almost 45,000 gallons of rainwater in a typical year.  This can meet most or all of the annual indoor needs of a water-conserving household of 3 to 4 people for a year.

Among the many benefits of rainwater use are: water supplies with few pollutants or treatment chemicals; elimination of scale in pipes and appliances (lengthening life and maintaining energy efficiency); and availability if emergencies curtail normal water service.    

Rainwater is mostly collected from the roofs of buildings.  It flows by gravity through gutters and downspouts into a storage tank.  From the tank it can be used in the landscape as is, or be filtered and treated to become a source of high-quality drinking water (though at this writing, rainwater is not officially permitted for indoor use in the City of Austin).

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Since most of our rainfall occurs in large storm events, the ability to store collected rainwater is paramount.  Storage ranges from small barrels of 50 gallons that can be placed at the end of storm gutters up to large tanks that can store 100,000 gallons.  All of the components for rainwater harvesting can be found in the plumbing section of area retailers.  Small rainbarrels can usually be found in garden stores.

A typical system replaces metal downspouts with plastic piping.  By making the downspouts watertight, water can be carried by gravity to a storage tank.  Several downspouts can be joined together into one larger main pipe leading to the tank.  This main pipe is usually buried below ground and breaks the surface again at the side of the tank.

An inlet to the tank is installed as high as possible to maximize storage capacity.  The inlet can be on the side or the top of the tank.  Just remember, the piping system (downspouts) at the building must be at least 6 inches (preferable 18 inches) above the highest piping at the tank.  This will allow the tank to fill, as the pressure of the water will work like a “P” trap under a sink.  The water will equalize and flow into the tank.  This “P” trap part of the system also must have an outlet installed to allow water to drain out for maintenance and to prevent freezing.

Keeping Rainwater Clean – Leaves, twigs, dust and bird droppings can be screened out of your system in several ways.  The simplest method is a first-flush filter.  The “first flush” of rainwater is sacrificed to make the rest of the water cleaner.  Each downspout can direct the water to a plugged pipe that looks much like the typical downspout, except it has a sewer clean-out plug at the bottom.

When the plug is in, the water fills the downspout until it reaches the top.  From here, the water is directed down to the collection pipe, which goes into the tank.  Each of these first-flush filters should be drained of debris after each rain to be ready for the next rain event.  If your tank is full, just open the sewer clean-out plug and the first-flush filter works like a normal downspout.

Other devices can be used to filter the water going into a tank.  Some are large, fiberglass boxes with 30-micron filters inside to screen out the particles.  Since these filters require cleaning and maintenance, using the first-flush filter ahead of them increases the time between cleaning or replacement.

Practical Use – A gravity system uses the water from the tank via water hoses, buckets, and soaker hoses.  It has very little natural pressure.  Even a drip-irrigation system needs at least 15 pounds per square inch.  You may eventually want to pressurize your system using the same components you see used on water wells: pump, pressure tank, and fine mesh filter.  This creates a more usable system, but adds to the overall cost and maintenance.

Rainwater for Drinking – A drinking water quality rainwater system costs about as much as the typical well.  With 20,000 to 30,000 gallons of storage, a family of four can be comfortable without a well or piped water service.  But families using rainwater as their sole source of potable water seldom have lush landscapes.

Much of the rain in Austin comes in downpours and your tank may be full and not able to capture all of a rainfall.  The time between rains can be long, so rainwater harvesting goes hand-in-hand with water conservation.

To make rainwater safe to drink, additional filtration is needed, plus perhaps an ozone system, reverse osmosis and/or ultraviolet irradiation.  The health of your family and guests depends on the design and safe operation of your drinking water system.

All Things Rainwater P.O. Box 2224 Wimberley, 78676 (512) 826-0653 Consultation, design, & sale of equipment
Austex Sprinklers 2000 Windy Terrace Bldg 22 Ste B Cedar Park, TX 78613 (512) 721-8564 1,500-3,500 gallons for irrigation; metal & plastic
Austin Gutterman, Inc 12229 Roxie Dr. Austin, TX 78729 (512) 450-1821 Up to several thousand gallons for gardens; plastic
Bowerbird Construction P.O. Box 1141 Dripping Springs, 78620 (512) 858-5395 20,000-100,000; ferrocement
Bright Leaf P.O. Box 300012 Austin, 78703 (512) 371-7220 500 gallons and up; all materials
Dick Peterson 3451 Mayfield Ranch, #306 Round Rock, 78681 (512) 922-3326 System design, consultation & instruction
Five Star Gutters & Services, Inc P.O. Box 5702 Round Rock, TX 78683 (512) 944-3924 Less than 1,500 gallons, most materials
Green Land Management, LLC P.O. Box 761 Dripping Springs, 78620 (512) 845-7024 Up to 100,000 gallons; all materials
Harvest Rain 2770 Hwy. 290 W. Dripping Springs, 78620 (512) 645-2955 2,500-190,000 gallons; all materials
Harvested Rain Solutions 11183 Circle Dr., Suite D Austin, 78736 (877) 693-2166 5-130,000 gal. irrigation systems; all materials
Innovative Water Solutions 501 W. Powell, Suite 206 Austin, 78753 (512) 490-0932 All types of materials
Lakota Water Company 10006 Longhorn Skwy. Dripping Springs, 78620 (877) 652-5682 10,000 gallons and over; lined-metal tanks
Luke’s Sky Water 13909 Panorama Drive Austin, 78732 (512) 920-2907 Residential; any materials
Native Constuction 201 Cole Street Austin, 78737 (855) 253-6284 20,000-30,000; metal
Pinnacle Water Tanks 1704 Colt Circle Marble Falls, TX 78654 (512) 755-4553 1,500-65,000 gallons; metal
Rainy Day Systems (512) 376-0097 Design, installation; all sizes; poly, metal, & fiberglass
Rainy Day Tanks 601 S. State Highway 95 Taylor, TX 76574 (512) 818-4626 100-5,000 gallon plastic; 3,000-250,000 gallon metal
Specified Water Systems, LLC P.O. Box 942 Dripping Springs,78620 (512) 301-5632 All sizes; lined steel & wood tanks
T&E Services 307 US Hwy 281 N  Johnson City, TX 78636 (512) 947-8191 Design/installation; residential and commercial; metal and plastic
Tall Drink Rainwater Harvesting 20310 Haystack Cove Spicewood, 78669 (512) 769-1254 6,000 gallons and up; metal and plastic
Texas Metal Tanks 16299 Fitzhugh Rd., Building E Dripping Springs, 78620 (512) 565-0875 90 to 5,000 gal.; metal & cedar
Texas Water Tank Systems LLC 7609 Davy Dr. Volente, TX 78641 (512) 673-7180 Up to 50,000 gallons; plastic, steel


Making Rainwater Cost Effective

Despite the many good qualities that rainwater systems have, they are quite expensive for small installations.  While a homeowner might justify cisterns in the country where they compete cost wise with well drilling, they almost never compete with municipal water supplies.  The one exception I have found is in, of all places, Boerne Texas, a small town about 30 miles north of San Antonio.

Boerne Champion High School built its unique system in 2006.24  It has a traditional metal cistern to catch run-off from the roof, but it also catches run-off from the 120-acre school site and stores it in underground pipes.  The water is aerated to keep it from turning septic, and is primarily used for landscape irrigation.  Add to this condensate from the school’s air conditioning system and natural spring infiltration, and the system can capture about 6 million gallons in an average year to meet the school’s need for landscaping.

Savings will pay for the $265,000 cost in about 6 years, even after considering operation and maintenance, making it cost effective compared to the cost of new water sources in some Texas cities.

Granted that this strategy will only work on large school or office complexes, it still points the way to a viable alternative that can probably work at dozens of sites in Central Texas.


Texas Manual on Rainwater Harvesting, Third Edition, July 2005.  On the Web at https://www.twdb.texas.gov/publications/brochures/conservation/doc/RainwaterHarvestingManual_3rdedition.pdf

City of Austin rainwater rebate program: austintexas.gov/department/water-conservation

Thanks to Austin Energy Green Building for assistance with this story.

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