How to build a high-volume residential rainwater harvesting system

These standpipes are also installed with a cleanout fitting at the bottom and should be emptied and cleaned out after each rainfall event. A pinhole drilled at the bottom of the pipe or a hose bibb fixture left slightly open allows water to gradually leak out, and the water from the standpipe may be routed to a planted area.

If you are using 3-inch diameter PVC or similar pipe for your first flush diverter, allow a 33-inch length of pipe per gallon; 4-inch diameter pipe needs only 18 inches of length per gallon; and a little over 8 inches of 6-inch diameter pipe is needed to catch a gallon of water. The recommendation ranges from one to two gallons of first-flush diversion for each 100 square feet of collection area. If you need more volume than vertical space allows, you can run your first flush diverter parallel to the ground by creating an elbow at the bottom of the assembly to make it bigger.

Conveyance piping

Conveyance piping connects the components of your system. You can use galvanized steel, aluminum, stainless steel, or high-density polyethylene piping, but the most readily available and cost-effective material is 3- or 4-inch diameter PVC piping. PVC can be found at most hardware stores, but it's not UV resistant, so any piping that isn't buried should be painted to prevent degradation from sun exposure.

Storage tanks (cisterns)

Cisterns store filtered rainwater above or below ground and, ideally, are opaque to prevent algae growth. Tanks are usually the most expensive part of every system and can be made of a variety of materials, including plastic, fiberglass, galvanized steel, concrete, and wood. Polypropylene and polyethylene tanks are common because they are readily available online and at farm and ranch suppliers, are cost-effective, and come in a variety of colors with capacities up to 10,000 gallons. For buried installations, specially reinforced tanks are necessary to withstand soil expansion and contraction.

Food-grade intermediate bulk containers (also known as IBC totes) are another storage option with a cheaper cost per gallon than most other tanks. If the water they hold is stored for an extended period, they should be painted or covered to prevent algae growth. Sand with 220 grit, apply "gripper" primer and two coats of flat exterior paint to keep UV light out, and you're good to go!

There are some key components to understand and install if your tank doesn't come already equipped. First, a calming inlet (the curled upward portion of pipe connected to the inlet at the top of the tank) is necessary to prevent incoming water from disturbing sediment at the bottom of the tank. Next is a floating pick-up (essentially a hose with a float attached to one end) for your outlet, which drains water from the top and prevents sediment from flowing into your irrigation system or watering can.

An overflow pipe is required to manage excess water when the tank fills and does double duty as an expansion port if you want to connect additional tanks to hold more water. Finally, the vent is necessary to prevent vacuum issues from plaguing the system during rain events. The vent, overflow, and other openings (if not connected to anything) on a tank should be covered with #24 mesh non-corrodible screen to prevent mosquitoes and other insects from getting inside-and note that the vent and overflow ports in the illustration are curled downward to keep out sunlight and prevent algae growth.

Pump system

A pump supplies pressurized water for irrigation. If you plan to run sprinklers or drip emitters, you'll need a pump that provides a consistent 30 psi of flow to connect to the tank outlet.

Installation and other considerations

When placing your tanks, the recommended installation is at least 24 inches away from any structure, at least 3 feet from any property line, and on a level surface. If you have a big tank, like a 5,000-gallon poly tank or larger, you'll need a slab or stabilized base.

Refer to your local building codes and soil load capacities to make sure your base is proper for the tank size and weight when filled with water. Pouring concrete is an option if you've consulted an engineer and know what size pad you need. Another option is to make a box frame using 6-inch-by-8-inch lumber and engineering structural screws, then fill it with compacted gravel.

Also, take time to consider the lay of your land and where the water from your overflow port, gutters, and first flush diverter will flow. You don't want to flood your neighbor's yard, and you do want to keep all that water on your property!

Constructing a rain garden with Texas native plants will absorb the runoff and pollutants while attracting songbirds and butterflies. Utilizing and creating passive retention features can direct water toward trees and other desirable parts of your landscape while rehydrating the soil.

Maintaining your system

Rainwater might be free, but keeping it flowing does come at a small cost-in the form of performing some basic maintenance on your system. Best practice is to check and clean any screen filters every 2 to 3 months. Every 6 months, clean your gutters and downspouts, rain heads, and first flush diverter. As you get to know your system, you can adjust your maintenance schedule.

Let's harvest some rain!

Now you know about the components and considerations required to design, build, and maintain your own medium-to-large scale residential rainwater harvesting system.

To learn more about rainwater harvesting, additional resources are available on the TWDB website, including a downloadable PDF of the Texas Manual on Rainwater Harvesting.

Because Texas wants to encourage conservation, the state has laws on the books to help reduce the construction costs of rainwater harvesting.

Texas Tax Code § 151.355 exempts rainwater harvesting equipment and supplies from state sales tax. To claim this exemption, fill out and furnish a Tax Exemption Application Form 01-339 to the supplier of the rainwater equipment. In addition to tax exemptions, your local government may have programs to reduce expenses as well.

Also, per Texas Tax Code § 11.32, the Texas Legislature allows governmental taxing units the option to exempt from taxation part or all 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. Check with your county appraisal district for guidance about county property tax exemptions for your system.