Rainwater catchment systems consist of three elements: the storage facility, usually made from tanks or barrels; the collection area, typically the roof of a house; and the transportation system, in the form of either some plain household gutters, or another kind of water-conveyance systems. Collecting rainwater is useful because you can harvest it for use in a home or garden, reducing your dependency on city-lines, or a channel connected to public utilities, making it a good, long-term investment that will cut your costs over time. However, it is especially important for use in gardening, because it is usually free of any minerals, harmful chemicals, or pesticides that might interrupt the delicate bio-cultures used in permaculture. It reduces your water bills, lowers your carbon footprint, allows you to store the rainwater for use in dry times, increasing your tolerance for droughts, and you can adapt household and yard products to serve a function within your system to catch rainwater. It is also expandable, and can be scaled up indefinitely, as short lengths can be used to link individual barrels together and boost the capacity of your system.
Before building the Rainwater Collection system, gather the following:
- 1x clean 30- to 55-gallon barrel or garbage can
- 1x S-shaped aluminum downspout elbow
- 4-6x concrete blocks
- 1x piece of aluminum window screen
- 1x standard 1 in. hose spigot with ¾ in. pipe threads
- 1x ¾ in. x ¾ in. coupling
- 1x ¾ in. x ¾ in. bushing
- 1x ¾ in. pipe thread with a 1 in. hose adapter
- 1x ¾ in. lock nut
- 4x metal washers
- 1x roll of Teflon thread tape
- 1x tube silicon caulk
- Pop rivet gun with rivets
- Pencil and ruler
- Adjustable, open end wrench
The containers you use could be any water-holding vessel, like recycled garbage cans, PVC containers, or food and water barrels. If you want a barrel made for holding rainwater, you can obtain one or more from specialty garden catalogs and online classifieds. To find one, check with companies that buy food ingredients in bulk. Some of their supplies come in large, seamless, plastic containers, which would make for easy-repurposing into a rain barrel. If you can’t find these barrels, you can substitute a big plastic trash can, or even a large polyethylene box. You could even have containers made from wood, metal, or fiberglass tanks. If you want, you can even build your own container. Barrels holding a volume up to 30-55 gallons (113.6-208.2 L) will suit the needs of most homes and small gardens. Consider your annual rainfall, the size and shape of the roof catchment area, and your personal water needs when determining the tank size. This system uses three standard 55 gallon drums, providing 165 gallons of water storage. Do not use barrels that once contained motor oil or fuel products, pesticides, or any other toxic substances. Be sure to scrub the inside of your container thoroughly with soap and water to remove any residues first.
The easiest way to collect rainwater is to channel the water that runs off of a broad sloped surface, known as a “catchment area.” One method to create a catchment area is by excavating a wide, shallow hole or basin at a point in a gully. When it rains, the water will pool at the bottom of this basin, as it runs down the paths in the ground, and can be collected by a conveyance system, like a tube or another connected channel, that transports the water down to a storage unit. Other options exist, but the most commonly used, and easily adapted, catchment area is the roof of a house. In some states that heavily regulate water collection and storage by individuals, may actually be the only legal catchment surface allowed for rainwater collection.
The size of your roof will determine how much water your system collects. On average, a house with a 1,000-square-foot (186 sq. m) roof collects about 600 gallons (2,271.2 L) of water per hour for every inch of rain, and approximately 25,000 gallons (80,000 liters) per year.
The kind of roof you have will also determine the quality of the rainwater you collect. The best kind is made from flat, wide metal sheets that repel the water downward to the gutters for collection. If you have asphalt tiles, you can also collect rainwater, although it will probably need a First-Flush filtering system to remove the broken-off particles from the tiles. To keep debris from washing into your gutters, install some gutter mesh, like Blue Mountain Mesh, on the gutters around your roof.
Start by picking a flat spot under a downspout close to your garden. If your area is located on open ground, clear away any rocks and other debris from the area and level it with a shovel. Then, dig a 4- or 5-inch deep rectangular trench in the area you leveled to accommodate the rain barrels, and fill it to the top with pea gravel. This will provide better drainage around the rain barrels and divert water away from your foundation. Skip this step if your downspout empties onto a concrete driveway or patio. If your chosen spot is situated on a hill, build a level surface by stacking some plywood boards in the low section until you’ve got a level area on which to set the barrels.
After laying down a layer of pea gravel as the foundation, and then start building the base by stacking concrete blocks on top to create a raised platform. Use this to hold the rain barrels, or build a wooden frame to hold them. The finished platform should be wide and long enough to hold all of your barrels, and be secured or steady enough so they won’t shift or tip over. Raising the barrels up higher also gets the spigot higher off the ground so you can get a watering can underneath it more easily. You can sit the barrels on the cinderblocks directly, or build a wooden frame to hold them above the ground, with or without the blocks.
The gutters and downspouts of your home can be integrated into a water harvesting system, conveying water to the reservoir. The downspout is the metal or plastic tube that connects to the gutter, and transports it down to the ground. Gutters and downspouts can be made from aluminum or plastic, although vinyl is probably the best material to use because it’s the easiest to work with.
Most houses already have a gutter system, with an accompanying downspout, or some form of piping used to expel the rainwater away from the foundation. However, most such arrangements are inadequate for the requirements of rainwater collection, and you may need to modify your gutters and downspouts in order to make your roof more suitable. For example, depending on the shape of your house, which kind of gutter you use, and the length of it, you may have to slope your gutters down towards the downspout that diverts the water into the reservoir. Normally, most gutters will have a downspout every 10 or 20 feet or so, but that is usually without a rainwater harvesting system installed. You may have to rework or rebuild your system to accommodate collecting water.
Regular downspouts direct water down from your gutters directly to your reservoir, but you can use a device called a downspout diverter to switch the direction of the flow of water. With this you can divert the flow of the downspout from the gutters (or the overflow spout from the holding tanks), to fill a channel that diverts to a swale or garden bed, for example. This is useful when you have variable rain during the seasons. There are also other alternatives to downspouts, one of which is a rain chain. This is a decorative water conveyance system that guides the rain from your roof down into your garden, watering can, rain barrel, or other rainwater collection system. They are usually made from copper or another metal, but can also be made using recycled or repurposed materials, such as metal buckets, tin cans, cups, chain links, garden ornaments, glass bottles, tea pots, or pretty much anything you can link together and use to convey water downward. A rain chain could also be integrated with plants for an automatic, self-watering, hanging vertical garden.
Regardless of whichever type you use, the gutters have to be large enough to carry the water that will run off the roof. Take special considerations in the case of high-volume storm water events that will overflow your gutters if they cannot handle the extra rainfall. The pipes used to bring the water down from the gutters, leading into the filters or storage tanks, should be wide enough to handle the rainwater coming from your gutters. Anywhere from 1 ½-3 in. wide pipes will do well for most houses. If you live in a high rainfall region, or one in which rain comes down in sudden bursts, you should have high capacity tubes or pipes that lead to the storage unit to handle the increased volume of water. If the water should become backed up, it could overwhelm your gutters and spill out over the sides, or weigh down the gutters to the point where their braces collapse. If you are using a traditional downspout, most home gutters are 5-6 in. wide. 3 in. diameter downspouts attach to the 5 in. gutters, and 4 in. downspouts go on 6 in. gutters. For roof collection areas up to 1,000 square feet, a 5 in. gutter with a 3 in. downspout should be large enough to handle the whole volume of water. Bigger roofs should have larger sized gutters and downspouts. Be sure to fit your downspouts and gutter outlets from the underside of the gutter to prevent obstructions.
Before being able to get the water into the barrel, it must be directed down from the gutters, and away from the house, with some connecting attachment, usually a downspout elbow. To measure where the downspout elbow will come out from the side of the house, start by setting the barrel on the blocks. Hold the new elbow about an inch or so above the top of the barrel, and make a mark on the downspout where it joins with the elbow. Set the barrel and elbow aside and measure 2 in. below the mark on the downspout. Use the hacksaw to cut the downspout, then fit the elbow on and fasten it with sheet metal screws or pop rivets. This will allow it to fit into the elbow with a good, solid connection.
To connect the storage unit to the conveyance system, extend the pipes or channels to the reservoir. If your barrel has a lid, use the hacksaw to cut a hole large enough for the end of the elbow to fit inside. Figure out where to connect the elbow to the downspout by setting the barrel on the platform next to the downspout. It should be close enough to the downspout so that you can connect it with the elbow so water will pour directly into the barrel. Mark the downspout one inch below the height of the rain barrel, and cut it with a hacksaw. Fit the elbow to the downspout, and fasten it tightly with screws.
After connecting the conveyance system with the barrel, drill a hole in the wall of the barrel near the bottom, but high up enough to put a bucket underneath to collect water. To match the standard size for a spigot, use a ¾ in. bit when drilling the hole. Another common sizing is 1 ¼ in., but if you’re using a different one, make sure you drill the right sized hole so that it fits seamlessly into the side of the barrel. Then, squeeze a ring of caulk around the hole on the inside and outside of the barrel. Slip a washer on the threaded end of the coupling and insert it through the hole in the barrel from the outside. On the inside, wrap Teflon tape on each of the threaded ends for a tight seal. Just wrap the tape around the pipe’s threads three times before screwing it into place. Then, put a washer over the pipe and fasten everything together with the bushing.
Next, install an overflow port near the top of the barrel, to which you can attach a hose to divert excess water out to the garden or use to connect additional barrels. Drill another ¾ in. hole (or the same size as the first hole you drilled) a couple of inches down from the top of the barrel. Squeeze a circle of caulk around the hole, inside and out. Then, place a washer on the hose adapter and push the assembly through the hole from the outside. Apply Teflon tape on the inside threads, slip a washer on the hose adapter, and attach a nut to tighten the assembly.
If you want to expand the system later on, you can connect more barrels to the first one by chaining them together in a linearly integrated system. This way, it will hold more water with each additional barrel. You have two options for this: you can either connect the barrels via their overflow valves so that as one fills with water, all the additional water spills over into the next one until that one fills up, and so on. The second method is to chain them together via holes on the bottom, and to only have one overflow valve on the top of the last barrel in the chain. If you want them connected via the overflow valves, simply connect them together with some hose or pipes. If you want them to be connected at the bottom, start by setting the barrels on the platform, and drill a third hole in the first barrel at the same level as the spigot, but several inches to the side. Next, drill a 3⁄4- in. hole in the second barrel at the same level as the hole you just drilled in the first one. Attach hose adapters to the holes in both barrels, and connect them together using some short lengths of a hose or pipe. If you’re using a third overflow barrel, the second barrel will need another valve on the opposite side, at the same level, so you can connect it to the third one. Consider leaving an air gap in between the tops of the tanks and the overflow outlets to prevent storm water backflow.
Water collected in open containers should be used quickly, or covered to keep out debris and animals. To prevent this, install a tank screen, or a fine-mesh aluminum window screen, over the entry point to your barrels. Then, cover the area around the hole with a metal screen at the top of the downspout. You can also construct a device to put over the downspout to serve as a screen, or buy a pre-built one from the store, like Leaf Eater or Leaf Beater rain heads. Attach insect-proof screens or flap valves at the ends of all pipes to keep bugs out and ensure the tank is properly vented.
Because some debris may be present in the rainwater, you may want to filter it before using it in your garden. If this is the case, install filters between the collection and conveyance systems to intercept and clean the water before it reaches the storage tanks. From there, you can use it for gardening or other uses, or even divert it off to be purified for drinking. For directions on possible filters, see the Aquaponics article for some applicable designs. A 300-micron nylon sock filter, placed over an inlet pipe inside a separate barrel, can be used as a sieve to remove most debris from the water.
One design you may need for rainwater collection is called a First-Flush filter. During storms, the residues on your roof (leaves, gravel, dust, etc.) will get washed off by the initial rain. These can clog up your conveyance systems or storage tanks over time. To prevent this, use what’s known as a First Flush Filter to separate much of this residue and debris out from the water before it gets into your tanks.
This filter consists of an empty 4 in. wide PVC pipe section. First, take a cut-off piece of a 3 in. wide PVC pipe, about 1 or 2 in. long, and wrap some rubber tubing around it to create a water-tight seal. Insert the 3 in. section into one end of the 4 in. pipe, and seal it in with caulk to create a step-down section in the diameter sizing of the entrance into the tube. On the other end, at the bottom, insert a removable plug to close it up. The plug should have a threaded end that, when screwed, pushes a rubber gasket out to create a water tight seal against the edge of the PVC pipe. After it rains, remove the plug to empty the filter and clean it out. Be sure to drill a small hole at the bottom of the 4 in. pipe, just above the plug, so that any water left inside will drain out after it rains.
Inside of the 4 in. tube, insert an object that floats in water, and thin enough to fit within the 4 in. tube, but too large to fit through the 3 in. section. You can also use a rubber ball or any other floating item that will create a seal between the two sections. The bottle sits at the bottom of the long pipe until it rains. Once it rains, the first gush of water goes into a section that’s separate from your reservoir, called the First Flush Filter. Most of the debris that washes off flows into and gets trapped in the 4 in. pipe. Water fills this pipe, and causes the object to rise up with the water until the pipe gets filled up. The object then seals the 3 in. opening at the top, and the remaining water, carrying less debris, then gets diverted into your rain tanks for collection, or additional filters, or another conveyance system to be carried off elsewhere.