What is rainwater harvesting?
Rainwater harvesting gathers rainwater and keeps it on site for later use. Rainwater capture can be used to provide water for landscaping and gardens, in-home use, wildlife, livestock, fire protection, stormwater management and rain gardens. We’ll share how to harvest rainwater including collection, storage and use, along with tips on maintaining your rainwater collection system and troubleshooting common problems. You can make a rain barrel in an afternoon and save water all season long.
Why is there a Need for Rainwater Harvesting?
Unlike many well water and municipal water supplies, rain water is naturally soft. Normal, clean rain has a pH of between 5.0 and 5.5. If you’re willing to invest in a rainwater harvesting system that meets your household needs, you can enjoy cleaner clothes and people, longer appliance life and no hard water buildup on fixtures and pipes.
In your garden, rainwater is the best option for your plants, because it’s free of salts and other minerals that can build up in the soil and harm your plants. Where groundwater is poor quality or unavailable, rainwater recovery may be your most affordable option for clean, safe water for you, your garden and livestock.
In urban and suburban areas, much of the surface area is made up of impenetrable surfaces (roofs, sidewalks, driveways, streets, etc.). Rainwater falls and is swept into storm sewers instead of slowly percolating into the soil. With rainwater capture and landscaping options such as rain gardens, we can keep the water on site longer and slowly release it into the soil. The more rainwater reclamation we have on site, the better we are able to manage stormwater, too. Municipal water also tends to be expensive, and many municipal water supplies are under stress, so if you can replace some of your water use with rainwater, it can save you money while you conserve water.
Is it Illegal to Collect Rainwater?
Some states do have specific laws on the books limiting rainwater harvesting or use, so it’s best to check with your local regulations before making a big investment. States with rainwater regulations include Arizona, Arkansas, California, Colorado, Hawaii, Illinois, Nevada, New Jersey, North Carolina, Ohio, Oklahoma, Oregon, Rhode Island, Texas, Utah, Virginia, Washington, and the U. S. Virgin islands. You can learn more at State Rainwater Harvesting Laws and Regulations.
Rainwater Storage Containers – Rain Barrels and Cisterns
A key component of your rainwater collection system is storage. Some options for rainwater storage containers include:
- Water barrels
- Stone cisterns
- Concrete or Ferro-Cement Cisterns
- IBC Tanks
- Metal Storage Tanks
- Polypropylene Storage Tanks
- Fiberglass Storage Tanks
In the book “Rainwater Collection for the Mechanically Challenged”, the authors recommend water barrels for small systems and fiberglass storage tanks for larger systems. The love the look of old stone cisterns, but they can be difficult to maintain and cost prohibitive to build new. Fiberglass cisterns are durable, UV resistant (which inhibits algae growth), budget friendly, and can be painted with household latex paint to create a decorative rainwater cistern.
Water barrels are a great way to start with rainwater harvesting on a small scale. They are budget friendly (you may be able to find the barrels cheap or free) so you only have to pay for the system components. For the rest of this article, we’ll focus primarily on rainwater harvesting systems with water barrels, but many of the concepts also apply to larger rainwater harvesting systems.
Finding Rain Barrels for Sale, Cheap Rain Barrels or Decorative Rain Barrels
Many home improvement stores now offer plain and decorative rain barrels and rain barrel kits, or they can be purchased through catalogs or online. There are decorative rain barrel options now, such as:
Where space is limited, there are rain barrels that are flat on one side to sit flush against a building.
For larger rainwater storage such as polypropylene or fiberglass tanks, check with farm supply or industrial supply stores. There are also some local programs that supply rain barrels at a reduced cost to encourage rainwater collection.
For free and cheap water barrels, inquire at local food processors. Often they receive ingredients in 55 gallon drums. For instance, we were able to get the barrels we used for our rain collection system for free from a nearby meat shop. Make sure you use FOOD GRADE BARRELS, not barrels that may have contained toxic substances.
Be Careful Water is Heavy
Recently I’ve seen a photo making the rounds of a rainwater collection system featuring three 55 gallon plastic drums, stacked on their side, one above the other, in a wooden frame with PVC connections. I don’t recommend that rain barrel system. Those bad boys are heavy, and they are hard piped. Once installed, it would be a bear to get in there and clean your barrels. If you have full barrels, you’re looking at over 1200 pounds of water. That’s an accident waiting to happen.
Some folks use garbage cans to make a rain barrel. I don’t recommend that, because garbage cans are not built to stand around full of water and chemicals may leach out of the plastic. Sooner rather than later, that garbage can rain barrel will end up as garbage itself.
How much rainwater will I collect?
If you cover one square foot with water an inch deep, it would equal 0.6233 gallons, which would mean that you could harvest 623.3 gallons from a 1000 square foot roof. Due to splashing and other losses, the book “Rainwater Collection for the Mechanically Challenged” estimates that a more realistic number is 550 gallons of rainwater harvested per inch of rain per 1000 square feet of collection surface. As you can see, a good rain can fill a water barrel pretty quickly, so make sure to include an overflow for your rainwater collection system.
Rain Barrel Stands
What do you do with rain barrels once you’ve collected the rainwater? You need to get access that water so you can use it in your yard and garden. As mentioned earlier, it’s great if you can position your barrel on high ground and gravity feed the water. Even without high ground, we want to get our rain barrels high enough that we can get a bucket under the spigot. This means we need a rain barrel stand.
Keep in mind that water weighs about eight pounds per gallon, so whatever you use for a rain barrel stand; make sure that it’s sturdy. A 55 gallon drum full of water will weigh over 450 pounds. You don’t want that tipping over on someone. You also want your stand to be level, to reduce the risk of tipping.
In our two rain barrel system, we paired up six concrete deck footings with a small reinforced treated wood deck. You could also use concrete blocks, or a combination of concrete blocks and pavers, as shown in the video below.
How to Make a Rain Barrel
Next up, we’ll go through the steps of making a rain barrel from a 55 gallon water drum. There are dozens of different ways to build a rain barrel system, as a quick online search will show you. Exactly how they collect rainwater varies, but there are three key elements in every system.
To make a rain barrel, you need:
- a way for the water to get in, with a screen to keep debris out
- a spigot to use your collected rainwater
- an overflow, in case your rain barrel gets too full
For a rain barrel system like ours, you need:
- 3/4” spade drill bit
- Utility knife
- 55 gallon plastic barrel
- ¾ inch faucet, brass preferred
- Fiberglass window screen
- Second ¾ inch faucet or PVC pipe for overflow
- Bulkhead fitting extension, to attach the faucet to the barrel
- Roll of Teflon tape and Caulk or plumbing sealant, if you encounter leaks, or to provide a more snug fit
For our rain barrel, we cut around the inside of the top ring, and inserted a sheet of fiberglass window screen to keep out debris. This is the simplest rainwater harvesting filter design you can use. I’ve also seen small holes cut in the top to fit a skimmer basket covered in fiberglass screen. Make sure your opening is big enough to capture the entire flow of rainwater form your downspout. You don’t want to have an open rain barrel, because this is an invitation to mosquitoes and other bugs. You will also want to be able to clean your filter or screen.
Do not skip the screen! I’ve seen “build a rain barrel” guides that don’t use a screen because they route the water directly into the barrel through a tight opening. Don’t do that! We have a high roof, with no trees around, and yet we still get bits of branches, leaves, tree seeds and other debris in our screen. I don’t know if the birds drop them or the wind blows them, but there is debris that would build up in your rain barrel or other rainwater harvesting container. You need at least a basic filter on your system.
Ideally, you would include a roof washing system that diverts the first round of rain from your roof around your barrels so you store cleaner rainwater. The book “Rainwater Collection for the Mechanically Challenged” has a great tutorial on building your own roof washer, or there are roof washer kits available online. If you want to collect rainwater for potable use, a roof washer is essential.
If you don’t want to reroute your downspout to the rain barrel, there are downspout diverter kits that insert into the side of a downspout, as shown in the video above.
Mark a spot at least two inches from the bottom of the water barrel. Why two inches above the bottom, instead of closer? That spacing will give you room to mount your faucet, plus it’ll help you avoid any sediment that builds up in the bottom of your rain barrel. Even with a screen, some sediment will build up – not a ton, but some. Our rain barrels are about 10 years old, and I scrub them out each year. They do get dirty.
If you get a good quality brass faucet, you should be able to screw it directly into the wall of your barrel wall once you’ve drilled your hole to match the faucet, as demonstrated in the video below. If you find that you need a tighter fit, or want to extend the faucet farther out, you can use PVC fittings and Teflon tape.
Rain Barrel Overflow
We have a two barrel system, with the first barrel connected to the second barrel via PVC fittings. The friend who built our rain barrel system fitted the overflow to the top of the second rain barrel because it was quick an easy, but it would work better located on the side, slightly above the PVC connection between the two rain barrels.
Whatever you decide to rig up for an overflow, whether it’s a hose or PVC fittings, make sure to route it away from your building, just as you would a downspout. You may even decide that you’d like to add a rain garden off of the overflow.
Maintaining Your Rain Barrel System
Because we have high winds, we added strapping to hold the barrels down when they're not filled. For winter, we drain the rain barrels and bring them into the greenhouse. Water expands about 11% when it freezes, so a frozen rain barrel is likely to have damaged fittings. If you don’t have a spot to move your rain barrels inside for winter, simply drain them and cover them so they can’t gather water or snow, and divert your downspout to its normal course. (We screw on a downspout extension for winter, and take it off again in the spring when the water barrels go out.)
In spring, before putting the rain barrels back into action, give the barrels a good cleaning. You want to scrub them out at the beginning of the season to make sure you're not starting off with contaminated water. Chunks and scum will clog up your faucets, and make your water foul.
For cleaning your rain barrels, you’ll need a long handled scrub brush, or you’ll have to crawl in to your barrel. I improvised by duck taping a piece of firewood to a brush with a shorter handle. Make sure to clean your screens, too, and double check that your faucet and overflow are clear of obstructions. (Sometimes spiders or other bugs move in during the winter.)
Algae in Your Rain Barrel
If you use a translucent barrel, you're more likely to algae growth due to sun exposure. Try covering your rain barrels with a tarp, painting your water barrels or using a wooden surround to block the light. If you're not opposed to goldfish in your rain water, they will eat the algae, as well as mosquito larva (see below). Just make sure that your rain barrels don't run dry!
Keeping Mosquitoes out of your Rain Barrels
Use a screen to keep mosquitoes from having easy access to your rain barrels. If you find that they still somehow manage to get in, a couple drops of vegetable oil on the water surface will prevent them from laying eggs. (Note, this will make your rain barrels messier so you need to clean them more frequently. You’ll also need to add more oil from time to time.)
Another option is to add a couple of goldfish to your rain barrel. They’ll eat the larva and add some fish poop fertilizer to your water. (Not recommended if you think you may need to drink the water.)
Mosquito dunks are another commonly recommended option, but not my top choice. The active ingredient in mosquito dunks is “Bacillus thuringiensis subspecies israelensis” (Bt), which attacks the larval stage of mosquitoes. This is a naturally occurring soil bacterium. There are concerns that Bt will be losing its effectiveness due to it being genetically engineered into corn and other crops.
It is Time for you to start Harvesting Rainwater with Rain Barrels?
Rain barrels are a great way to control run off and conserve water. Rainwater lacks chlorine and fluoride that is found in many municipal water supplies. Natural rain water is softer and easier on your garden plants.
My grandmother always washed her hair every Saturday night with water from her rain barrel. If you happen to have a good water filter such as a Berkey, you can use rain barrel water for drinking water in case of emergencies.
If you want to learn more about how to design your rainwater harvesting system, plans for roof washing systems, and just about any other questions you may have on rainwater collection for household use, I recommend the book “Rainwater Collection for the Mechanically Challenged“.
Do you have rain barrels or another rainwater harvesting system? How do you have yours set up, and how do you use your rainwater? I’d especially love to learn more from those who use rainwater for household and livestock use.
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Originally published in 2011, updated 2016, 2018.