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Rainwater harvesting is the capture, diversion, and storage of rainwater for a number of different purposes including landscape irrigation, drinking and domestic use, aquifer recharge, and stormwater abatement. In a residential or small-scale application, rainwater harvesting can be as simple as channeling rain running off an unguttered roof to a planted landscape area via contoured landscape. To prevent erosion on sloped surfaces, a bermed concave holding area down slope can store water for direct use by turfgrass or plants. More complex systems include gutters, pipes, storage tanks or cisterns, filtering, pump(s), and water treatment for potable use.

Rainwater Harvesting Q&A

Just hover your cursor over the photo to see the answer for each question.

What are the basic parts of a rainwater harvesting system?

  • Catchment surface: the collection surface from which rainfall runs off, typically a roof on a home or building

  • Gutters and downspouts: channel water from the roof to the tank

  • Leaf screens, first-flush diverters, and roof washers: components which remove debris and dust from the captured rainwater before it goes to the tank

  • One or more storage tanks, also called cisterns

  • Delivery system: gravity-fed or pumped to the end use

  • Treatment/purification: for potable systems, filters and other methods to make the water safe to drink


What are the benefits a rainwater harvesting system?

  • The water is free; the only cost is for collection and use.

  • Rainwater provides a water source when groundwater is unavailable, or it can augment limited groundwater supplies.

  • The zero hardness of rainwater helps prevent scale on appliances, extending their use.

  • Rainwater is superior for landscape irrigation.

  • Rainwater harvesting reduces flow to stormwater drains and also reduces non-point source pollution.

  • Rainwater harvesting reduces consumers’ utility bills.

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How much water can I capture?

  • The basic rule for sizing any harvesting system is that the volume of rainwater is that can be captured (the supply) must equal or exceed the volume of water used (the demand). In theory, approximately 0.62 gallons per square foot of collection surface per inch of rainfall can be collected. In practice, however, some rainwater is lost to first flush, evaporation, splash-out overshoot from the gutters in hard rains and small leaks.

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How do I get started with a rainwater harvesting system?

Rainwater collection systems can be as simple as collecting rain in a barrel or as elaborate as harvesting rainwater into large cisterns to supply your entire household. Rainwater storage systems and equipment can be purchased at local home improvement stores, lawn and garden stores, and even ordered online!

A great resource for you to use is the Texas Water Development Board's Rainwater Harvesting guide. Just click the link below to download a PDF of that guide. Plus, you might want to read the Tax Exemption information as well.

The Trinity Glen Rose District put together a "how to" video for building your own rain barrels. Check it out below.

TGR Rain Barrel Construction Video

Safety First!

Safety is always a must when working with power tools. So, we strongly recommend you wear a pair of safety glasses or some sort of eye protection during this project.


Where to find an empty barrel:

Tools needed:

  • drill - 3/8 to 1/2 hp

  • Paddle (spade) bit, 15/16" and 2 3/8" hole saw

  • Set of hole saws or a jigsaw to make a 6" hole in the top

Materials needed:                                                                

  • A ¾” brass faucet (hose bibb)

  • 2” male PVC connectors & electrical Nut

  • Tube of silicone (bathtub)

  • Barrel​

Step 1 - Drill a hole in the top of the barrel for rainwater to flow into.

Mark a spot in the top of the barrel. It doesn’t have to be the middle. Use a 6” hole saw to cut it out. Or using the bottom of a one-gallon plastic pot, mark a circle around the bottom of the pot.  Drill a ¼” hole on one side of the circle and saw the circle out.  Saw to the outside line you drew with the plastic pot.

Step 2 - Drill the overflow hole.

Using the pot as a depth gauge, mark and drill the overflow hole just beneath the depth of the pot. Use the 2 3/8” hole saw.  

Step 3 - Drill a hole for the hose bibb. 

About 3 inches up from the bottom of the barrel, drill a 15/16” hole for the 3/4” hose bibb. 

Step 4 - Install the hose bibb. 

Put a little silicone around the threads on the hose bibb, push down and screw it in.  It will be sealed when you finish. Be sure to point the hose bibb to the side for better access. About 3 inches up from the bottom of the barrel, drill a 15/16” hole for the 3/4” hose bibb. 

Step 5 - Install the overflow. 

Insert the 2” adapter with the male threads through the hole. Thread the 2” electrical nut on adapter inside of the barrel.

Step 6 - Screening out debris.

Place mosquito screen in bottom of pot & add rocks (about 2-3 inches deep) and place it in the top of the barrel.  This is the filter to keep out the large stuff off the roof. 

Step 7 - Connect your rain barrel to the downspout.

Place your rain barrel in a location where it will capture rain running off of the roof. Or, you can attach a diversion to your existing downspout that will direct water into the barrel.

Other Considerations

  • Level your barrel!!

  • Elevating barrels provides room for watering cans and increases gravity flow

  • If linking barrels together, place an overflow pipe on last barrel

  • Pond Pumps and transfer pumps can be used to increase flow

  • Consider placement of faucet if you live in a windy area

  • If you have children, strongly advised to anchor the barrel to your home

Connecting two or more barrels together is easy!

1.If you want to hook two or more barrels together, use the overflow hole as the hookup between the barrels.​

2.Use a piece of 2” PVC pipe with a male-threaded connector glued to the end and screw it into the female fitting on the inside of the first barrel.  Do the same thing on the other end of the pipe and on the next barrel until all the barrels are hooked up.

3.If you do the same setup on the bottom of all the barrels, the water will empty out of all the  barrels at the same time.  PLUS, you only need one hose bibb in one barrel.

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