Rainwater harvesting project, saving up to £500 per year

Hi I'd like to share a few thoughts about a large (120,000 litre) rain harvesting project we are working on at out home.

We have the potential for storing up to 120,000 litres. The nice garden we've created turns out to be a very costly thing to irrigate through the year. Also with global warming etc etc it does seem to be a very logical thing to do in order to save resources on site and minimise use of town water.

It is also better for the plants.

The basics are an A frame roof structure with six 100 mm downpipes. Our plans are for either several reservoirs of totalling about 2,000 litres capacity placed within the basement area or a much larger single preformed tank sitting round the back of the house.

We are very fortunate in that we are able to tap into main (dedicated) drains from the top 3 and maybe 4 downpipes and then use downpipe attachments to get the water from the lower 2 or maybe 3.

The potential is enormous, the outlay minimal and the overall effect has to be beneficial.

However we have several question marks.

The door to the basement is less than 80cms wide so we'll have to hack into the walls to get the reservoirs, probably 3 or 4, into there. we have found some fancy ones made in several parts which clamp together with seals but even they would be hard to get into the space.

So we go for the single large one placed either above or partially sunken round the back of the house. Maybe a preformed tank or possibly use a cheaper septic tank.

As we live on a hill with the garden at the bottom it would seem to be ideal for using the water by gravity only. Maybe we may set up a smaller store with a pump feed from the main store at a future date so we can water the garden area higher up around the house.

Does anyone have any experience of such projects? Love to hear from all.

One specific question is has anyone ever used a preformed septic tank for such (water storage) use? Are they strong enough?

Lou

I was puzzled to hear you were thinking of putting the water storage in the basement of the ?house?

If you're going to the expense of constructing a basement, I would have thought you'd get better value using it for living and storage. You could have an underground RC tank in the garden with less expense and disruption. I suppose like a simple swimming pool but roofed over.

BTW, fallout shelters are exempt from Planning Permission and Building Regs, so you might think about a dual-purpose hole in the ground.

JohnD said:

I was puzzled to hear you were thinking of putting the water storage in the basement of the ?house?

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It's a bit of an extra space, not required for much and sits higher than much of the garden outside. apart from the access problem, it is ideal for any storage use, including water!

Fallout? alas I one of the people that think we are on our own self-destruct with climate change and from that there is no shelter!

However you never know what chaos this may cause and stand pipes in the road as the only source of water may be a lesser disturbance than having to empty the water tank in the threat of an air raid.

I’m assuming that this is not an April fool.

I have looked into rainwater harvesting myself but on a much smaller scale. The size of the tank I have calculated would be 3,500 litres. If I did go ahead with the idea, it would cost about £2,500 supply only for a tank, pump, filters, vermin traps, mains-water top-up etc.

Type “Rainwater” and “Harvesting” into Google and stacks of web sites will appear.

I was going to use the water from mine for irrigation, toilet flushing and laundry – NOT potable use as this would need UV sterilisation, plus the roof area for my house would not give off enough water for all my needs – I could do rainwater harvesting AND then do greywater harvesting. One step at a time though!

Sticking a 120,000 litre tank in your basement – would that not be problematic from a weight point of view? Also, it is a good idea to allow the tank to overflow two of three times a year to stop water stagnating. How did you arrive at your tank size? Catchment area plays the largest part in tank size followed by water usage (I think a figure of 8% of annual usage was quoted on one web-site I looked at).

Let us know how you get on.


G

120,000 litres thats a big tank!

not sure of the size you are thinking of, but many commercial storage tanks used for normal water storage in offices etc come as sectional kits which are bolted together, so averting the problem of getting it through the door.

Bear in mind that 1m x 1m x 1m of water is approximatley 1 tonne so it might be worth getting some advice with regards the loadings on the floor slab.

Big G said:

Sticking a 120,000 litre tank in your basement –
G

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Don't think I said a tank that size, that's the potential rainfall to collect!

We think 3,000 litres plus. However logistics mean several smaller coupled together underneath the house or one huge one partially buried ouside the back.

Interestingly because of the hill situ I go for a simple, low cost set up which may be expanded in the future. This is 1 or 2 cubic metre tanks in the basement to start, cost under £800. This is usable for the main garden area on gravity feed. Then another £1000 or so for a 3 cubic metre tank set into the top of the hill fed from the smaller units by pump and then used by gravity.

Not bad for a simple installation.

lou

I would also check with your local water board as more and more of them are now against rain water harvesting. They prefer the water to go to ground or down the drain as more goes back to them for treatment .

lionleg said:

I would also check with your local water board as more and more of them are now against rain water harvesting. They prefer the water to go to ground or down the drain as more goes back to them for treatment .

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They may be against it, but after all it is your water and they do charge you both for fresh water and to take away the rain water!

Put in as much storage as you can fit! We have a 3000 litre tank and its pants. We (family of 5) use it for toilets and washing machine. I would say we need at least 4 times that storage based on our usage.
Also if you are using it for gardening then consider that your hose sprays up to 1000ltrs an hour at mains pressure.


Also watch for "system losses" we have a Klargester (envireau) system and simply in order to run the pump it needs 1500 litres of water in it so there is very little space left to store water. At the moment we are looking at digging out the tank thats fitted and putting in a 12K or bigger tank.

don't go for the fancy ones made in several parts which clamp together with seals unless its above ground and with easy excess, those tanks leak mostly round the base.

daysleeper said:

Also watch for "system losses" we have a Klargester (envireau) system and simply in order to run the pump it needs 1500 litres of water in it so there is very little space left to store water. At the moment we are looking at digging out the tank thats fitted and putting in a 12K or bigger tank.

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surely thats just bad desighn!!!!

all you need is a sump a self priming pump with a float switch and a few litres of water

surely thats just bad desighn

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you might say that, but as its likely to all be in the hands of lawyers very soon I could not possibly comment.

daysleeper said:

surely thats just bad desighn

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you might say that, but as its likely to all be in the hands of lawyers very soon I could not possibly comment.

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oooohhhhh dear

couldnt you just interlink it with another tank at the same level with a propper sump and get over the problem that way!!!!!

couldnt you just interlink it with another tank at the same level with a propper sump and get over the problem that way!!!!!

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Theoretically yes, but stuffed if I'm paying for it. The maufacturer recommended a system thats inappropriate and supplied a system does not work as advertised.

As far as I'm concerned they can pay to replace it.

Grr Argh

daysleeper said:

couldnt you just interlink it with another tank at the same level with a propper sump and get over the problem that way!!!!!

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Theoretically yes, but stuffed if I'm paying for it. The maufacturer recommended a system thats inappropriate and supplied a system does not work as advertised.

As far as I'm concerned they can pay to replace it.

Grr Argh

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yes i agree its there problem i just thought if they made such a fundamental mistake they may not have a clue as to a solution

so you might get another pump /sump/and 1000Ltank for nowt fitted