With the country in the grip of a disastrous drought, here’s how to save those precious drops when they do fall with a DIY rainwater harvesting system.
Words and Pictures: Stephen Smith
Water. So taken for granted until those shortages hit home. But instead of just playing the waiting game and anxiously watching the horizon, get outdoors and do what you can to gather any rain that falls by making your own rainwater harvesting system.
How does this rainwater harvesting system work?
The rain saver is essentially two drums plumbed together to form one water container. A tap allows a hosepipe to be joined to them, while a hole in the top of one drum allows for rainwater to be delivered via a gutter’s downspout.
Top Tip: You could add a third or even fourth drum in series to increase the volume of your tank.
How to create your own rainwater harvesting system
You will need
- 2 x 95-litre plastic drums, or something similar. Make sure they’re UV stabilised. Black refuse bins would also work.
- 20cm x 20cm plastic insect mesh
- PVC Weld
- 2 x 90° gutter elbows, to fit your existing gutter system
- 2 x geyser tray spouts
- 1 x Gardena hose-pipe connector
- thread tape
- 1m x 50mm PVC pipe
- 1 x 50mm PVC T-joint
- 2 x 50mm PVC 90° elbows
- 2 x 15mm nylon nipples
- 1 x 32mm to 15mm male to female nylon reducer
- 1 x 20mm to 15mm male to female nylon reducer
- 1 x female thread 15mm ball valve
- 1 x 50mm to 32mm female PVC plain/threaded adapter. (This can be confusing. It needs to have a smooth 50mm female side to fit the PVC pipe and a 32mm threaded female side).
- Electric drill, cordless drill/screwdriver; 50mm holesaw; 10mm drill bit; screwdriver bit; scissors; jigsaw and fine blade; pencil, hacksaw
Optional wooden stand
You’ll need something to stand your water tanks on. Bricks, cinder blocks or even a table will work perfectly, as long as you make a gap for the plumbing (or put the plumbing in the sides of the drums instead of at the bottom). We decided to make a small wooden table for the task, out of scrap wood we had lying around. It was recycled from a large wooden pallet and didn’t cost us a penny.
- 2 x (900mm x 80mm x 60mm)
- 6 x (180mm x 80mm x 60mm)
- 4 x (500mm x 80mm x 60mm)
- 32 x (6mm x 120mm cut screws)
Cost: About R1 300, excluding the wood for the stand. If you can source second-hand drums, you could save a substantial portion of this. Ours cost R360 each.
Difficulty: 2 out of 5
Time: A morning (having an extra pair of hands will make this project easier.)
Make a hole in the lid of one of the drums. The drums we used had circular marking on the lids, which made the job easier. If yours don’t, trace a circle of about 150mm in diameter in the middle of the lid.
Drill a 10mm hole just inside this line and use it as a starting point for your jigsaw. Cut out the circle with your jigsaw (a fine blade makes for a neat cut in plastic) to create an opening for the water to be delivered.
If you’re worried about mosquitoes, silicone a piece of plastic mesh to the inside of the lid, covering the hole.
Turn both drums upside-down. Using the 50mm holesaw and the drill (proper, corded electric drills cope better with holesaws than cordless drills), make one hole in the centre of the bottom of each drum.
It’s now time to start the plumbing, which is a bit like the ‘knee bone is connected to the thigh bone’ song. To make sure that everything fits in the end, do a dry run, fitting everything together without glue. Start with the geyser tray spouts.
Unscrew the connectors, insert the ends through the holes in the bottom of the drums from below. From the inside of the drum, screw the connectors back on the spouts. You may need a hand with this, with your assistant holding the spouts still while you screw on the connectors.
Cut two pieces of 50mm PVC pipe about 80mm long. Push one into one of the geyser spouts. To the top of this PVC pipe connect the PVC 90° elbow. Repeat this on the other drum. Now you need to do some measuring. With the drums still upside down and placed next to each other, face the two elbows towards each other.
NOTE: All our lengths of pipe were cut to length to fit the two drums we used. If you use different drums, you will need to adjust these measurements accordingly.
You need to connect these two elbows together using 50mm PVC pipe, but with a T-joint in the middle. You also need to take into account that the PVC pipe will go into the two elbows and the T-joint, about 20mm at each joint, so don’t forget to add this to your measurements.
We cut two 150mm lengths of 50mm PVC pipe. Place one pipe into one elbow, then repeat with the other elbow. Join these two pipes together using the T-joint. Remember, this is just a dry run, so if you have made these pipes too long you can undo it all and trim the pipe, or replace it with a longer piece if it is too short.
Cut a piece of 50mm PVC pipe to about 220mm. Insert this into the third opening of the T-joint. Onto the end of this, pop the 50mm side of the PVC plain/threaded adapter. Into this screw the 32mm end of the 32mm to 15mm male to female reducer. Into this screw one of the 15mm nylon nipples.
To the other side, screw on the 15mm ball valve, followed by the other 15mm nylon nipple. Now screw the 15mm female side of the 15mm to 20mm reducer to the nipple. Finally, screw on the 20mm Gardena hosepipe connector. You’re almost there!
This is an important step. Take a step back from your plumbing and give it a fresh look. Are the barrels close enough together? Are all the joints in the correct sequence? Are all the pieces of the PVC pipe the correct length? If they are, carry on to the next step.
Before final assembly, you need a base on which to place your water tank. We quickly knocked one together out of treated 80mm x 60mm pine that we recycled from a large pallet.
If you want to make a similar one, join the two 900mm pieces together with two 180mm pieces, one at either end, to make a rectangular frame. Screw these into place using the 120mm cut screws. About 200mm in from these two end pieces, add the other two 180mm pieces.
The top of your stand is done. Screw one of the 500mm pieces to each corner as legs. Your stand is complete.
Remove the geyser spouts from the two drums. Place the drums on the stand and replace the geyser spouts, just to check that everything fits onto the stand and the plumbing doesn’t get in the way. The T-joint should be angled down at about 45°, to miss the stand, but there should still be space under the hosepipe connector for a bucket.
If everything fits into place, pat yourself on the back. Good job so far. Now take all the plumbing apart, but keep it in the correct sequence. It’s time to glue. Put the geyser spouts into position. Squeeze some silicon around both surfaces where they come into contact with the drum to form a seal and screw them into place.
Put all the PVC fittings and pipes back into sequence, but this time use PVC Weld to glue them into place. When you get to the threaded fittings, put away the PVC Weld and pick up the thread tape. Wind thread tape onto each male thread, then tightly screw all the connectors back into place, finishing with the hosepipe connector.
With the assistance of your able mate, carry your newly completed rainwater harvester to the selected gutter downpipe. Place it into position and make sure it is level and stable. When its full it will weigh about 200kg, so you don’t want it tipping over.
Using the hacksaw, cut the gutter downpipe just above the hole in your tank. Pop on a 90° elbow, then the piece of the gutter you have just cut off. Cut this pipe off above the hole in the tank and add the other 90° elbow, directing water into your tank.
TIP: Choose a gutter downpipe at one of the higher points of your garden, so that you can use gravity to reach most of your garden with a hosepipe.
Finally, add an overflow pipe, using a section of the leftover 50mm PVC pipe. In the wall of one of the tanks, near the top, drill a 50mm hole with the holesaw. Push the pipe into this hole and silicone into place, so that it directs any overflow away from the tanks and into the garden. Do a rain dance and prepare to be amazed at how quickly your tanks fill up in even a light rain.
- Rain, and even dew, adds up very quickly and your tanks will fill up in no time. As an example, if there is rainfall of just 10mm, a roof of only 10m² will harvest about 90 litres.
- If the names of all the plumbing fittings get confusing, take this article into your local hardware store and show them the pictures. They will easily be able to help you get the correct bits together.