Frequently Asked Questions
- What is rainwater harvesting?
- Why is there so much interest of late in rainwater harvesting?
- What service does the TWDB provide to individuals or communities interested in learning about rainwater harvesting or implementing a rainwater harvesting program?
- Does the TWDB provide funds to communities interested in installing a rainwater harvesting system?
- 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?
- Are there any laws or rules governing the construction, operation, and maintenance of rainwater harvesting systems?
- How much does a rainwater harvesting system for a typical single-family home cost?
- Are there any tax breaks for installing a rainwater harvesting system?
- Are all rainwater collection systems above-ground?
- Where can I get information on manufacturers of rainwater harvesting systems?
- I have a flat roof. Would a rainwater harvesting system be a viable option for me?
- Why should I be interested in rainwater harvesting when there is so much water that is readily available for my use?
- Where can I see an installed rainwater harvesting system in Austin?
- Is collected rainwater safe to drink? Does it have to be inspected or tested before being used?
- 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?
- What are some of the benefits of rainwater harvesting?
- What are some of the limitations?
- Is rainwater harvesting a water management strategy that has to be considered by regional water planning groups for their plans?
- When and where was the first rainwater harvesting system built?
- What other countries are actively pursuing rainwater harvesting?
- Whom can I contact at the TWDB for more information on rainwater harvesting?
Answers to Frequently Asked Questions
1. What is rainwater harvesting?
Rainwater harvesting is the capture and storage of rainwater for landscape irrigation, potable and non-potable 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: its 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 by-products, 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 TWDB 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 Texas Manual on Rainwater Harvesting was published in 2005 and is available online in pdf format (2.42 MB). Other rainwater harvesting information and some useful links are 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 non-profit 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 that they can avail of (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. Most installers use an efficiency of about 75 to 85 percent for the system.
For your Austin home, using a collection rate of 0.62, a system efficiency of 0.85, and an average annual rainfall of 32 inches, you can expect to collect about 34,000 gallons of rainwater per year (0.62 x 0.85 x 2,000 x 32 = 33,700 gallons per year). Using these same parameters for the El Paso location but with an average annual rainfall of 8.5 inches, the amount of water you can expect to collect will be only about 9,000 gallons (0.62 x 0.85 x 2,000 x 8.5 = 8,950 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 non-potable 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 inter-agency 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, 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 ( 1.57 MB) published in 2004 by the Texas Water Development Board provides some guidelines for water providers on rainwater harvesting and condensate reuse.
More recently (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 §341.042) include a requirement that:
- A rainwater harvesting system connected to a public water supply system that is 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 TCEQ.
- 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 $0.5 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 Texas Constitution, Article 8, §1-m, the Texas 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 Texas Tax Code §11.32, the Texas 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, Texas Tax Code §151.355 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 at http://www.window.state.tx.us/taxinfo/taxforms/01-339.pdf.
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 (2.42 MB).
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 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 American Rainwater Catchment Systems Association Web site has useful information on manufacturer's and service providers of rainwater harvesting systems.
11. I have a flat roof. Would a rainwater harvesting system be a viable option for me?
Yes. If the roof has a drain that can channel the rainwater, the roof can be used.
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 over-abundance 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 by-products, salts, minerals, and other natural and man-made 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?
There are several non-residential rainwater harvesting systems in Austin that are available for public viewing. The Lady Bird Johnson Wildflower Center at 4801 La Crosse Avenue 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 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 ( 2.42 MB).
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 on to 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 water quality standards for harvested rainwater. However, appropriate county health department and city building staff should be contacted for local testing requirements prior to using rainwater for drinking purposes.
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?
There are currently no federal or state plumbing standards for rainwater harvesting systems that are not connected to a public water supply system. However, legislation passed in 2011 requires that a person who installs and maintains rainwater harvesting system that is connected to a public water supply system and is 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 (Texas Health and Safety Code §341.042).
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 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 challenges?
Some of the challenges 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?
Texas Water Code 16.053(e)(5)(C) 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 4500 BC in parts of India and the Middle East. In China, rainwater harvesting was being practiced almost 6000 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 Matt Webb at 512-463-6929.