Rain Water

Rainwater Harvesting

For centuries, people have relied on rainwater harvesting to supply water for household, landscape, livestock, and agricultural uses. Before the advent of large centralized water supply systems, rainwater was collected from roofs and stored on site in tanks known as cisterns. With the development of large, reliable water treatment and distribution systems and more affordable well drilling equipment, rain harvesting was all but forgotten, even though it offered a source of pure, soft, low-sodium water.

A renewed interest in this time-honored approach of collecting water has emerged in Texas and elsewhere because of escalating environmental and economic costs of providing water by centralized water systems or by well drilling. The health benefits of rainwater and potential cost savings associated with rainwater collection systems have further spurred this interest.

Texas is one of only a few states in the nation that has devoted a considerable amount of attention to rainwater harvesting and has enacted many laws regulating the practice of collecting rainwater.

Texas Tax Code 151.355 allows for a state sales tax exemption on rainwater harvesting equipment.
Texas Property Code 202.007 prevents homeowners associations from banning rainwater harvesting installations.
Texas House Bill 3391 requires rainwater harvesting system technology to be incorporated into the design of new state buildings and allows financial institutions to consider making loans for developments using rainwater as the sole source of water supply.


Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the main supply. It provides water when there is a drought, can help mitigate flooding of low-lying areas, and reduces demand on wells which may enable ground water levels to be sustained. It also helps in the availability of potable water as rainwater is substantially free of salinity and other salts.


Here at iBuild we make sure the concentration of contaminants are reduced significantly by diverting the initial flow of run-off water to waste.  In addition, the improved water quality can also be obtained by using a floating draw-off mechanism (rather than from the base of the tank) and by using a series of tanks, which draw from the last in series. The stored rainwater may need to be analyzed properly before use in a way appropriate to ensure its safe use.

We understand that the quality of collected rainwater is generally better than that of surface water and that contamination is always possible by airborne dust and mists, bird feces, and other debris, so we ensure that treatment of the water is in place, depending on how the water will be used.

System setup

Rainwater harvesting systems can be installed by iBuild with expert technicians. The system should be sized to meet the water demand throughout the dry season since it must be big enough to support daily water consumption. Specifically, the rainfall capturing area such as a building roof must be large enough to maintain adequate flow. The water storage tank size should be large enough to contain the captured water.

Design Considerations

When you start thinking about a catchment system for your home or business, you’ve first got to answer the question, “How big?”  iBuild will calculate the amount of water usage your family will need.   A catchment system can be as small as a single 50 gallon rain barrel or as large as an underground cistern of 50,000 gallons.  From one rain barrel to a linked system of 5 or 10 rain barrels, the thinking is the same:  collect the water from a downspout on your roof and store as much as you can.

With water rates climbing rapidly, and with drought conditions around us, it will make sense to catch and store as much water as possible. You can probably collect more than you can store.

Types of Tanks and Tank Stability

While a vast majority of the rainwater collection storage tanks are placed above ground, there are tanks available that can be installed below ground surface. In-ground storage tanks tend to be a lot more expensive than above-ground tanks because of excavation costs and the need to have a more heavily reinforced tank.
Water weighs just over 8 pounds per gallon, so even a relatively small 1,500-gallon tank will weigh 12,400 pounds. A leaning tank may collapse; therefore, tanks should be placed on a stable, level pad. If the pad consists of a stable substrate, such as decomposed granite, a load of sand or pea gravel covering the bed may be sufficient preparation. In some areas, sand or pea gravel over well-compacted soil may be sufficient for a small tank.

Calculating Storage Tank Size

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 an average home with a roof surface of 2,000 square feet, using a collection rate of 0.62, a system efficiency of 0.85, and an average annual rainfall of 32 inches per year in Austin, you can expect to collect about 33,700 gallons of rainwater per year (0.62 x 0.85 x 2,000 x 32 = 33,728 gallons per year).  So, even if you only collect from half the roof in a drought year (0.62 x 0.85 x 1,000 x 32 = 16,684 gallons per year), you still can collect a lot of rain water.  You just need a tank large enough to store it.


There are various methods determine the amount of rainwater you should collect to meet your needs. The easiest method to calculate landscape water use is to look at your past water bills and compare winter months water use to summer water use each month. The portion of higher water use in the summer is most likely that amount used for exterior landscaping. Some very rough, but simple daily consumption guidelines are:

  • Gardens/Lawns 600 gallons per 1,000 square feet
  • Young Trees 15 gallons
  • Small Animals .25 gallons per 25 pounds
  • Dairy Cattle 20 gallons
  • Range Cattle 15 gallons

Whatever your type of system you desire, iBuild has the solution.