15 February 2018
Installing tandem rainwater tanks
There are many contractors who are offering to install rainwater storage tanks in businesses and in homes, but it is not difficult to do the job yourself – you simply need to know how. So, here’s how…
First of all, we have avoided being too specific regarding number of components, lengths of downpipe and so on, simply because every situation will be different, and individual needs will vary as well. So we are going to deal in broad strokes and will show you how to install a tank – or tanks yourself, thereby saving on contractor’s fees – which can vary from very reasonable, to downright exorbitant.
But lets first deal with all things contractor related:
There are many out there who are reasonable, they do a great job and are reliable, so if, despite reading this article, you decide to go with a contractor, do so. Keep these in mind when making the right decision…
- Ask your local Mica for advice on who they advise offers the best service.
- Get three contractors to visit so that you can establish the best position for the tank/s. Ideally the position should be as unobtrusive as possible, but also be as close as possible to the largest area of roof, preferably on the weather side of your home.
- Get at least three itemised quotes – the tank/s, piping from gutters, various taps and fittings you will need in order to make use of the water you will store. In this regard, make sure you are VERY precise in what you want, and know EXACTLY what you will be getting for your money. Then make sure that the quotes cover precise materials required for the foundation, lengths of piping required, and the exact type and number of fittings.
- From each contractor from whom you obtain a quote, ask for three references. Call them and where possible ask if you can visit to see the work for yourself. This will give you and idea of the contractors work.
- If your neighbours have already had tanks installed, ask them who they used and what they thought of the service, standard of work and the costs.
- Having decided on your contractor, commission them and agree on payment terms – but do not pay the entire amount upfront. The usual method is 50% on signing and the balance once the work is completed to your satisfaction.
- It is also as well to obtain and undertaking that should any leak develop with the fittings within a year or so, he will sort them out at no cost. After all, it is usually only when the tanks approach full capacity that you will be able to confirm everything is watertight.
Doing it yourself
One or two: Why install two tanks instead of just one? The two tanks featured here are relatively large (950ℓ each) and by linking them with a simple system of ballcocks and piping, you could use both simultaneously, or one at a time, and if a leak should develop in one, you could isolate it and at least save some of my stored water. Linking them also allows me to make the best possible use of the entire roof – even a small section of it over the main bedroom – on the weather side of the house.
Where to put them: The larger the collection surface, and the closer to horizontal it is, the better, so these two tanks are on the north-facing, weather side of the house, and will collect rainwater from an area of about 14m² over the main bedroom (3.5m of roof 4m long) plus a further 48m² over the second bedroom, lounge, dining-room (one continuous roof 4m wide by 12m long) giving a total collection area of approximately 62m².
How big: The size of the tank/s depends on your perceived needs, space available for them, your budget and so on, but a visit to your local Mica will enable you to get a very good idea of what’s available, capacities, prices and so on, but our suggestion is: Sooner rather than later… at the time of writing this piece the demand for tanks in Cape Town meant a delivery delay of as much as eight weeks depending on the tank/s required.
In short, tanks range in sizes and capacities from 260ℓ [620mmØx925mm high] up to as large as 20000ℓ. However, as a homeowner you will most likely be looking at the range between the above-mentioned 260ℓ and the 5000ℓ [1820xxØx2255mm high] – a visit to your local Mica will enable you to get some answers as to what is best for you.
Colour: Manufacturers produce tanks in a range of colours selected to be as pleasing on the eye as possible. See what’s available and make your choice. The tanks featured here are a colour called ‘winter green’, a light beige that fits in well with the home’s wall colour and the surrounding garden foliage.
As mentioned above, the materials you will require will vary according to your particular needs, but as a rough guideline, here are the materials required for the installation featured here:
Eight 20kg bags of ready mix concrete (this foundation is about 75mm thick); ten 1.8m lengths of treated timber 22x69mm; one bag of 40mm stainless or decking screws
- • Two 950ℓ tanks
- • Three 3m lengths of round 80mm downpipe
- • Two shoes
- • Three 80mm 90° bends
- • Seven mounting brackets
- • Three 40mm ballcocks
- • One 3m length of 40mm soil/vent pipe (if you can try to get only a metre or so, but often pipes – as per the 80mm downpipe mentioned above are sold only in lengths of 3m)
- • One 40mm ‘T’-piece
- • Two 40mm nipples
- • Two 40/20mm reducing nipples
- • Two 40mm 90° bends
- • Two push-on fittings
- • Two barbed male adapters
- • Thread tape
- • PVC cement
- • Tie-down (optional):
- 3mm steel cable, four cable clamps, two hooked or eye rawl bolts.
Note: The materials you require will almost certainly differ, so get advice from your local Mica as to exactly what is required.
- Choose the spot for your tanks and remove all vegetation – grass, plants etc
- Smooth the surface. The spot should be as level as possible. I also used a spare paving slab to block off the downpipe drain.
- Set out the border for your foundation – to ensure that the sides are at 90° to the existing wall, use the 3-4-5 triangle method you learned at school – Pythagoras’s theorem… the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.
- This is optional, we wanted to shape the outer corners at 45°. So we cut a couple lengths of 22x44mm SA pine as shown here.
- This is how they fit across the corners.
- The completed mould. Note the use of the level to ensure the timbers are level.
- We mixed the concrete as per the manufacturer’s instructions and poured it into the mould. (Try not to use too much water in the mix, follow the manufacturer’s instructions.)
- Constantly check that the surface is level in both directions.
- We gave the surface a light sweeping to smooth it, and checked again that there were no low or high areas, and dealt with them as necessary.
- The completed foundation. A very light sprinkling of a little water over the surface will confirm how level the surface is; if you notice any noticeable flow, puddles or islands, then you need to do some adjustment.
- The manufacturers recommend that the concrete be kept wet for seven days so we used quadruple layers of shade cloth to slow drying out under the hot sun and kept it wet.
- We wanted to also use a treated timber base in the installation as we plan on later adding a trellis around the tanks for creepers. The instructions state no gap wider than 50mm, so we selected a gap of 16mm.
- We needed 10 lengths of 1.8m, nine of which we then trimmed down to the required length of 1.7m.
- Line them up and anchor the first and last at the required width and check that they are true by measuring the diagonals; if they are equal, then both end planks are exactly aligned and parallel.
- We ripped the tenth plank down its centre for the connecting battens for the timber base and used a single screw per end to secure each plank at the right interval from its companions. (Once the tanks are full, nothing will move those planks.)
- The tanks in position on their concrete and timber foundation.
- The home’s original downpipes were rectangular in shape, so the first thing to do was shape the one end of one of the downpipes, which we had cut to a length of 400mm and then used three lengths of the timber offcuts hammered into the end and the application of a heat-gun to shape the end.
- The downpipe in position.
- Then we cut a 90mmØ round hole in the tanks’ lids for the end of the shoes.
- This type of tank comes complete with a leaf trap, but it is a little hard to grip, so we made up a simple nylon cord handle. (Later on I also added a long leash and attached the handle to the lid as the trap can fall into the tank if not aligned, at least now it can be retrieved easily should it fall in.)
- We added a swan neck to a short length of downpipe as shown, and a shoe to the lower end into the tank. This unit is not glued to the gutter downpipe so that it can be removed, allowing the lid to be removed and the leaf trap removed and cleaned.
- Ready to collect when it rains.
- Now for the far side, we reshaped the neck of one half of a swan-neck and attached it to the gutter as shown here.
- The pipe to the tank had to be further away from the wall due to two pool solar-heater pipes down the wall.
- We made up four brackets using aluminium angle and pop rivets as shown to provide clearance of 80mm from the wall and attached them to the brackets.
- If there is a run on plumbing supplies due to the crisis, and bends are in short supply, you can make up a 90° bend as shown here, but using a shoe and a 40mm length of 80mmØ downpipe, split as shown. Use PVC cement to weld the one part to the other, but ensure that the split will be at the top of the pipe when the bend is in position. When a pipe end is slipped into position the gap at the split is minimal as the pipe end is hard up against the end of the shoe, and can be sealed, but it’s still best of the split as at the top.
- A shoe is added to the end of the flared end of the downpipe cut to length and that is slipped over the end of the bend as shown here so that, as per the first tank, the pipe can be removed when necessary.
- Once installation is completed, connect the tanks – these are the components: the two 40mm black bushings are screwed into the tank fitting, using thread tape to make the joins watertight. The 40mm ball valves are screwed on to the bushings, and then the push-on fittings are screwed on to the outer ends of the ball valves.
- We cut two short lengths of 40mmØ soil/vent pipe to connect the push-on fitting to the 90° bends as shown here. Do not glue them on yet.
- The two ball valves attached to the tanks’ outlets. Now is the time to ensure the valves are aligned properly.
- The completed outer section; even allowing for perspective, the connecting cross-pipe unit is a little long – rather do it this way, it’s easier to cut the two connecting piped short, than try to join on extra lengths. Do a dry fit to confirm exactly how much needs to be trimmed off.
- We took the total length to be trimmed off, divided it in half, and trimmed both connecting cross-pipes as shown.
- Complete all your treaded connections (using thread tape on each one to ensure no leaks. Then apply cement to the 40mm 90° bends and ‘T’-piece –ensuring that they are exactly aligned. Finally, apply cement to the outer ends of the push-on connectors and firmly push the connecting cross-pipe unit on to them. Both tanks are now connected; you can use water from both, or individually and isolate one tor either tank when necessary.
- As an optional extra and given that these are tall, slim tanks and Cape Town is known for high winds, We also secured the tanks to the wall using hooked rawl bolts and 3mm steel cable secured with two cable clamps on each end. This will probably not be necessary if you install tanks of a squatter design.
- The installation was completed by closing off each tank’s top 40mm fitting with a cap and adding a 20mm stopcock to each tank’s feeder fitting (it’s at about knee height). Usually one would make the connection simply by using a single 20mm nipple, but they were out of stock. So, making a plan, I used two 15/20mm reducing bushes and a 15mm nipple on each to make the connection. Note the use of thread tape to seal the thread. A hose or pump fitting, as required, is then fitted to the outer end of the ballcock.
- And finally, a note about the downpipe wall brackets: usually for a home (other than double-storey dwellings) only two brackets are necessary when attaching a downpipe to the wall… one at the top where the pipe meets the swan fitting from the gutter, and the other at its foot when the shoe is fitted at the drain. However, when attaching downpipes as in this feature – namely horizontally, to feed rainwater from distant gutters, use brackets at intervals of about a metre or so. Fine debris comes off the roof with every shower and if the pipe sags at all between brackets this can be deposited, impeding the flow. So brace it with more brackets as shown here to keep it on the straight and narrow.
These materials are available at Selected Mica Stores. To find out which is your closest Mica and whether or not they stock the items required, please go to www.mica.co.za, find your store and call them. If your local Mica does not stock exactly what you need they will be able to order it for you or suggest an alternative product or a reputable source.
- • TIME: 2 days
- • COST: Very dependent on the size and number of tanks you install and the amount of ducting you might need to do.
- • Skill: 2
- • Assistant: To help you move the empty tanks into position.