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The first issue is deciding on how you will collect the water. In the UK, every square metre will capture 100cm of water. That makes the maths quite easy so each m2 of roof space will – over a period of a year – on average gather 1m3, or 1000 litres of water. http://www.bom.gov.au/hydro/has/FAQ.shtml My best options were to gather water from the back pitch of my house: 28m3, and the back pitch of the garage roof, 14m3. I could probably add the front of the garage roof, but the front pitch of the house would require extra pumping and underground pipework, requiring a level of commitment that I wasn't prepared to put in. I estimate that provides me with an approximate potential of 42,000 litres over the year to collect. However the rain patterns are such that the barrels fill up and some portion of the rain is wasted. In the photo on the right, I used the B&Q Sankey rainwater collector high up on the down pipe and used cheap solvent weld overflow pipe (21.5mm) to channel the water to the barrels behind my garage. The other pipe, next to the bird box wrapped in insulation is the high pressure pipe work to the rain water tank in the loft, we'll come to that later... |
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Rain water fills the barrels from the top pipework (rear house roof), and the right side which is from the garage roof. |
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All the barrels are connected in a bus arraignment. If your into Computing/Electronics you'll understand what mean by that, basically they're all joined together at the bottom in parallel on the same level plane so they fill up and empty at the same rate. This pipework is standard 22mm, push fittings, normally I would choose copper but the convenience of these new plastic fittings and that fact that I wanted this work completing ASAP, plastic was the way to go. Currently, as a write this, copper prices are very expensive but the plastic fittings are more so. The barrels I chose are a B&Q SanKey variety holding 210 litres each. They're very cost effective when you compare that a 900 litre tank currently retails for £400 on the B&Q site. Since that photo was taken, I have 1200 litres of storage and to be honest, that's not enough. Once or twice last year, I ran out, and I reckon if you have a large family you'd want to (at the very least) double that capacity. A large underground tank will become a sensible option if you really do want to take this seriously. You should keep the water dark with the lids on to stop algae growth, and keep foreign objects out. |
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Rain is dirty, it collects with particulates on the way down. You will need a filter of some description. I used a ScrewFix filter for £18, but I do not use the activated carbon filter that came with it. Instead I've used the cheaper sediment filters (part numbers 65989 and 69860), they both fit I've tested them and they work well. You can see from the photo after a few months how dirty the water is, I generally change them after 6 months. |
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In the back of the garage I've got a “water pressure booster pump”. I got this from a company called Just Off Base, on amazon.co.uk, which bizarrely was cheaper then buying it direct from the Draper website. Note that the pump is higher than the water barrels, so the system needs priming before operating. Water enters the back of the garage and can be controller by the quarter turn valve. Water can be shut off to change the filter. Originally, I had a check valve next (that's a non-return valve or one way valve) but this failed once when a small leaf got trapped in it cause the pump to become staved of water. I've since corrected that so the filter is before the check valve. The great advantage of using this Water Pressure Boost Pump is that it maintains mains water pressure automatically. There is a pressure sensor on the back of the lower pressure vessel that activates the pump when water pressure falls below 30psi, and switches off when 45psi is reached. The great benefit now is that you can use standard mains water pressure parts for the rest of the plumbing that are, cheap and readily available should they require repair. From the top of the pump I've got mains water pressure, that gave me a tap in the garage for washing the car / bikes, and the other pipe goes into the house loft space and fills a standard 100 litre loft cold water tank. The pump must not be allowed to run dry, so in the black box above the pump is a relay connected to a float switch which is located in one of the barrels outside. The system must be shutdown on frosty days. The black box has a spare input for a thermostat, I've not yet found a suitable device that will power off the system when the ambient temp is less than < 3oC. |
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The tank is located in the loft, it's standard apart from: I've re-enforced the side where the water enters, the tank only came with one plastic re-enforcement strap anyway so If there isn't enough rain water, main water is used to top-up the tank, this is the pipe on the left. The pipe on the right is the feed from the rainwater booster pump. All pipe work should be supported, do not leave mains pressure pipe to “hang” supported by their compression fittings. Check the tank for leaks before fitting in the loft. The tank must be insulated, I've removed that in the photo. If using plastic pipes, read the instructions relating to the correct use of olives, and pipe liners. All rain water pipe work should be marked a non-portable water. |
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Make sure the base for the tank is well supported, and the insulation underneath it removed. 100 litres = 100Kg, and that's heavy. Obviously if you don't think your roof timber will handle the extra weight, or you have doubts, you should use a smaller tank. |
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Inside the tank, this is the float valve from the rain water feed. This is a stock part unmodified. Don't forget to hook up the overflow system, that's the white plastic pipe behind the float valve. Follow all instructions that came with the tank regarding height fittings of all valves/overflow/breather items.
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This is the main water feed. I've modified a standard float valve so that the float is continuously submerged. I had to lengthen the brass arm using another float valve and solder them together to get arm to an acceptable depth. When the rain water is not functioning, the water level in the tank will drop to the point where it will start to fill from mains water. No one in the house should be inconvenienced. |
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