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Rainwater Harvesting FAQ

How much does it cost to install a rainwater harvesting system? Is that water safe to drink? And how much rainwater can a homeowner really expect to collect?

  • August 1, 2012
Woody Welch
John Kight's rainwater harvesting system at his home in Boerne has been in operation since 2001 and has not run dry, not even during last year's drought. He's become a rainwater evangelist who will rave about the many benefits he enjoys from collecting his own water. Among them: crystal-clear ice cubes and a drink that's like liquid satin on the tongue.

The Texas Water Development Board, the state agency whose mission is to provide leadership, planning, financial assistance, information and education for the conservation and responsible development of water for Texas, offers answers to common questions about rainwater harvesting.

1. What is rainwater harvesting?

Rainwater harvesting is the capture and storage of rainwater for landscape irrigation, potable and nonpotable indoor use and storm water abatement. Harvested rainwater can be particularly useful when no other source of water supply is available, or if the available supply is inadequate or of poor quality.

2. Why is there so much interest of late in rainwater harvesting?

Rainwater harvesting is enjoying a revival in popularity for two reasons: rainwater’s inherently superior quality and an interest in reducing consumption of treated water. Rainwater has long been valued for its purity and softness. It is slightly acidic and is free from disinfectant byproducts, salts, minerals and other natural and man-made contaminants. Furthermore, rainwater harvesting is valued as a water conservation tool to reduce demand on more traditional water supply sources.

3. What service does the Texas Water Development Board provide to individuals or communities interested in learning about rainwater harvesting or implementing a rainwater harvesting program?

The TWDB has published a technical guide on rainwater harvesting. The latest version—The Texas Manual on Rainwater Harvesting—was published in 2005 and is available online in PDF format. Other rainwater harvesting information is available on our Useful Links page.

Currently, due to staff and resource limitations, the TWDB can offer only limited technical assistance to communities and individuals interested in rainwater harvesting. This level of effort may increase in the future to include educational workshops, seminars and conferences.

4. Does the TWDB provide funds to communities and individuals interested in installing a rainwater harvesting system?

The TWDB provides financial assistance for water supply projects regardless of the technology used. Eligibility criteria and requirements vary depending on the program but typically favor large-scale projects proposed by nonprofit water supply corporations, water districts, municipalities and governmental institutions. Private organizations and individuals are not eligible to apply for financial assistance from these programs. For private individuals, there are a number of other financial incentives available (see Question 8, below).

5. I have a home with a 2,000-square-foot roof in Austin and another in El Paso. How much water can I expect to collect at each location in a year?

In theory, a rainwater harvesting system can collect approximately 0.62 gallons of water per square foot of roof area, per inch of rainfall. In practice, however, there is always some loss due to first flush, evaporation, splash-out, overshoot from gutters and possible leaks.

For your Austin home (average annual rainfall, 32 inches), you can expect to collect about 34,000 gallons of rainwater per year. For the El Paso location (average annual rainfall, 8.5 inches), the amount of water you can expect to collect will be only about 9,000 gallons.

6. Are there any laws or rules governing the construction, operation and maintenance of rainwater harvesting systems?

At present, there are no national standards or regulations for rainwater harvesting systems. In Texas however, several laws have been passed in support of rainwater harvesting.

In 2005, the 79th Texas Legislature established the Rainwater Harvesting Evaluation Committee (HB 2430) and directed the TWDB and three other agencies to formulate recommendations for minimum water quality standards for potable and nonpotable indoor use, treatment methods, conjunctive use with existing municipal water systems, and ways in which the state can further promote rainwater harvesting. A TWDB representative served as the chairperson of this interagency committee. The committee provided its report of recommendations to the Legislature on December 1, 2006.

One other law that may be of potential interest for homeowners interested in installing a rainwater harvesting system is HB 645 passed by the 78th Texas Legislature in 2003. This law prohibits homeowners’ associations from implementing new covenants banning rainwater harvesting installations but grants them the authority to develop and implement rules requiring homeowners to screen their systems appropriately.

The Water Conservation Best Management Practices Guide published in 2004 by the TWDB provides guidelines for water providers on rainwater harvesting and condensate reuse.

In 2011, the Legislature passed several pieces of legislation that relate to the installation of rainwater harvesting systems. Some notable provisions (more information available in Texas Health and Safety Code include a requirement that:

• A rainwater harvesting system connected to a public water supply system used for potable indoor purposes is required to have cross-connection safeguards to ensure that harvested rainwater does not come into contact with the public water supply system’s drinking water off the property, in accordance with rules to be developed by the Texas Commission on Environmental Quality.

• A person intending to connect a rainwater harvesting system to a public water supply system for potable purposes must receive the consent of the municipality in which the rainwater harvesting system is located or to the owner or operator of the public water supply system before connecting the rainwater harvesting system to the public water supply system.

• A person who installs and maintains rainwater harvesting systems that are connected to a public water supply system and are used for potable purposes must be licensed by the Texas State Board of Plumbing Examiners as a master plumber or journeyman plumber and hold an endorsement issued by the board as a water supply protection specialist.

7. How much does a rainwater harvesting system for a typical single-family home cost?

A complete rainwater harvesting system for a typical single-family home will generally cost between $8,000 and $10,000. The single largest cost in a rainwater harvesting system is the storage tank. As expected, the cost of a tank depends on its size and construction material. On a per gallon basis, this cost can range from about 50 cents for a fiberglass tank to more than $4 for a welded steel tank. Other components such as gutters, downspouts, roof washers, pumps, and pressure tanks will add to the cost of the system. Professionally installed systems can further increase costs. If the intended use of the system is to collect water for drinking, costs for disinfection must be added to the total cost.

8. Are there any tax incentives for installing a rainwater harvesting system?

Under the Texas Constitution, the Legislature may authorize a taxing unit to grant an exemption from property tax for property on which a water conservation initiative has been implemented. In the Texas Tax Code, the Legislature allows governmental taxing units the option to exempt from taxation part or all of the assessed value of property on which water conservation initiatives are made. The taxing entity designates by ordinance or law the eligible water conservation initiatives, which may include rainwater-harvesting systems. Individuals planning to install rainwater harvesting systems should check with their respective county appraisal districts for guidance on exemption from county property taxes.

In addition, the Texas Tax Code exempts rainwater harvesting equipment and supplies from state sales tax. To claim this exemption, a purchaser of rainwater harvesting equipment must furnish a Tax Exemption Application Form 01-339 (back of form) to the supplier of the equipment. The form may be found online through the Texas Comptroller of Public Accounts.

In addition to tax exemptions, the City of Austin offers rebates and discounts to customers who install rainwater harvesting and condensate recovery systems. More information about this program and other similar programs is available in the Texas Manual on Rainwater Harvesting.

9. Are all rainwater collection systems above ground?

While a vast majority of the rainwater collection systems installed in Texas are indeed above ground, there are systems available that can be installed below ground surface. In-ground storage tanks tend to be more expensive than above-ground tanks because of excavation costs and the need to have a more heavily reinforced tank.

10. Where can I get information on manufacturers of rainwater harvesting systems?

The City of Austin’s water conservation website has useful information on manufacturers of rainwater harvesting systems. A list of manufacturers is also available from Green Builders, and HarvestH2O.com.

11. I have a flat roof. Would a rainwater harvesting system be a viable option for me?

Yes. As long as the roof has a drain that can channel rainwater, water can be collected for use.

12. Why should I be interested in rainwater harvesting when there is so much water already available for my use?

It is a fallacy that there is an overabundance of water available for our use in the state. The population of Texas is expected to double over the next 50 years, and existing surface water and groundwater resources are being depleted. Already, there are places in Texas that are experiencing shortages because demands are greater than available supplies. Rainwater harvesting provides us an opportunity to conserve and extend our existing resources.

Also, rainwater has some intrinsic qualities that should make it attractive to the user. It is pure, soft and only slightly acidic. It is also free of disinfectant byproducts, salts, minerals, and other natural and artificial chemicals that are typically added to water from centralized water supply systems. Plants tend to thrive under rainwater irrigation, appliances last longer because the water is salt-free, and the water tastes good because it is relatively free of chemicals.

13. Where can I see an installed rainwater harvesting system in Austin?

Several nonresidential rainwater harvesting systems in Austin are available for public viewing. The Lady Bird Johnson Wildflower Center has a 70,000-gallon rainwater storage tank that supplies almost 10 to 15 percent of water to the center’s landscape. The H-E-B store at 6900 Brodie Lane in Southwest Austin has a rainwater harvesting system with a 28,000-gallon storage capacity. The water is used for the native and adapted plants at the location. Several other locations in Austin and in other areas of the state are described in the Texas Manual on Rainwater Harvesting.

14. Is collected rainwater safe to drink? Does it have to be inspected or tested before being used?

Collected rainwater is generally safe to drink after treatment. As rain falls through the atmosphere and onto the catchment surface, it may pick up microbial and chemical contaminants and particulate matter. These contaminants must be removed before the water is used. Currently, there are no federal or state standards for harvested rainwater quality unless the system is designated by the TCEQ as a public water supply system.

15. Does the plumbing for a rainwater harvesting system that I plan to install in my home have to be inspected before the first use, and annually?

As mentioned earlier, there are currently no federal or state standards for rainwater harvesting systems. However, recently passed legislation (2011) requires that rainwater harvesting systems connected to a public water supply system that are used for potable indoor purposes have cross-connection safeguards to ensure that harvested rainwater does not come into contact with the public water supply system’s drinking water. Furthermore, a person who installs and maintains such systems is required to be licensed by the Texas State Board of Plumbing Examiners as a master plumber or journeyman plumber and hold an endorsement issued by the board as a water supply protection specialist. Rules for these requirements are currently being developed by the TCEQ and the Texas State Board of Plumbing Examiners.

Lastly, a person who intends to connect a rainwater harvesting system to a public water supply system for use for potable purposes must give written notice of that intention to the municipality in which the rainwater harvesting system is located or the owner or operator of the public water supply system before connecting the rainwater harvesting system to the public water supply system.

We also strongly urge homeowners to contact local and county officials for guidance on construction requirements.

16. What are some of the benefits of rainwater harvesting?

There are a number of benefits to using water from rainwater harvesting systems:

• The water is practically free: the only cost is to collect and treat it.

• The end use is located close to the source, thereby eliminating the need for costly distribution systems.

• Rainwater provides a source of water when a more traditional source such as groundwater is unavailable or the quality unacceptable.

• The zero hardness of rainwater helps prevent scales from building up on appliances and so extends the life of appliances.

• Rainwater is free of sodium.

• Rainwater is superior for landscape use and plants thrive on rainwater.

• Rainwater harvesting reduces flow to storm sewers and the threat of flooding.

• Rainwater harvesting helps utilities reduce peak demands during summer months.

• By harvesting rainwater, homeowners can reduce their utility bills.

17. What are some of the limitations?

Some of the limitations of rainwater harvesting are:

• Because rainfall events are highly unpredictable, rainwater harvesting cannot be relied on as a long-term, drought-proof source of water supply.

• The capital cost for a rainwater harvesting system is typically higher than the cost of obtaining water from a centralized distribution system. However, it is comparable to the cost of drilling and installing a new groundwater well.

• Rainwater harvesting systems require care and maintenance after installation which may not be suitable for all homeowners.

• Rainwater storage tanks may take up valuable space around the house.

• In Texas, rainwater harvesting systems are not subject to state building code and the absence of clear construction guidelines may discourage homeowners and developers from installing these systems.

18. Is rainwater harvesting a water management strategy that has to be considered by regional water planning groups for their plans?

The Texas Water Code requires regional water planning groups to consider all potentially feasible water management strategies including those that develop new supplies. Water collected through rainwater harvesting could be considered to be a new supply and hence a potential water management strategy.

19. When and where was the first rainwater harvesting system built?

Archeological evidence suggests that rainwater was being collected for use as early as 4,500 B.C. in parts of India and the Middle East. In China, rainwater harvesting was being practiced almost 6,000 years ago. In Texas, Mescalero Apaches used natural rainwater catchment systems near El Paso nearly 10,000 years ago to collect rainwater (“The Brethren of Cisterns” by Robert Bryce).

20. What other countries are actively pursuing rainwater harvesting?

Rainwater harvesting is being actively pursued on almost every continent of the world. It is most prevalent in the developing countries of Asia, Africa and Latin America where dependence on seasonal rain necessitates that water be collected and stored where and when it becomes available. Even developed countries in Europe and the Americas such as Germany and the United States have started harvesting rainwater as available traditional supplies dwindle or become contaminated.

21. Whom can I contact at the TWDB for more information on rainwater harvesting?

If you need more information about rainwater harvesting systems, please contact Sanjeev Kalaswad at (512) 936-0838 or Jorge Arroyo at (512) 475-3003.

For additional information, view the Texas Water Development Board website.

TWDB-funded UT-Austin research on the effect of roof materials on harvested rainwater quality

Map of Priority Groundwater Management Areas (PGMAs) from TCEQ website