What an amazing amount of rain here in Stroud today and last night!  Judging from the depth of rainwater collected in various containers, it was at least 2 inches.  I’m not complaining – just what the allotment and particularly the potatoes were needing.

I’ve been setting up a LOT of rainwater storage in my garden, with old re-used industrial containers called IBCs (stands for International Bulk Container).    These tanks hold 1000 litres each (over 250 gallons, or about 5 normal garden water butts’ worth).   You can buy them on ebay – the tanks are usually around £50 each but the delivery can be costly depending on how far away they are.  I was lucky (sort of, see below)  with my 3, they were £30 each from Bristol and only £25 total for delivery.    I was also lucky with the timing.  I only got the second one set up yesterday evening, and now it is full!  I collected 1400 litres of water in the last 24 hours from the house roof, and could have collected more if the third tank had been in place sooner.   The aim of all this rainwater is mainly for watering the polytunnel and the outside plants in pots and trays that I’m raising to sell.    This is all new – I only moved into my house last Autumn and only got the polytunnel  finished at the end of May, which is why I’ve only just set up my rainwater storage tanks in July.

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(The IBCs will later have light-proof covers made from bamboo matting or hessian or wood, to prevent  growth of algae and breakdown of the plastic due to sunlight.)

Nerdy IBC details

Two vital things I’ve learned about IBCs from buying these ones:

1. IBC Outlets come in 2 sizes – 60mm is normal, 100mm is rare.  Mine all have 100mm outlets which made it much more expensive to buy the fittings to attach garden taps and hoses.  If I’d bought tanks with 60mm outlets I could have bought screw-on IBC adapters with garden taps for a fiver each on ebay.  The only place I could get 100mm adapters and taps was Smiths of the Forest of Dean at more like £25 each.
2. Avoid containers that have been used for glue etc!    I’d only asked the seller to confirm that the tanks hadn’t contained anything toxic, but I should have been more thorough.  Mine had contained PVA glue which hadn’t been washed out very well and had set in places – YUK.  So avoid IBCs which have had anything in them which is either poisonous or which sets if not properly washed out!

Update 7 years on (May 2021)

A reader contacted me a few days ago with the following questions about the IBCS:

“Have you found the IBCs to be a good, long term option?
I currently have green plastic water butts and they weather pretty well; don’t become brittle and are generally pretty sturdy.
The plastic of the IBCs looks like it might become brittle over time.Do you ever clean them out and is it a complicated process?Have you found that the weight of the tank when full is too heavy for the earth it sits on?”

So I thought that now would be a good time to post an update to this article, saying how the IBC containers have worked out as part of a garden rainwater storage system for the last 7 years.  Here’s my reply to Amy’s questions:

“Yes, I’ve found the IBCs to work very well long term, and I would recommend them as a solution. I have three in my garden. They all stand on concrete or paving stones, and are raised up on bricks or concrete blocks. I wouldn’t put them straight onto the soil or grass – I agree that you’d need to spread the load (full, they each weigh one tonne). On the other hand, if you do put them on bricks or blocks straight on the soil, and they sink a bit, it’s not a big job to do it again, so you could just try it and hope for the best. But on balance, if they’re going onto soil, I’d suggest paving stones under the concrete blocks or bricks.

They are all boxed in with featheredge fencing boards to protect the plastic against degradation by UV, and they look very neat. (Tip: fix 3×2 timber to the frame with garden wire, then screw the featheredge boards to the 3×2). Two have a roof over the top, and the third just has some landscaping fabric on top held down by wood scraps, to keep the UV off the top. I’ve never cleaned them out, but I do have a system of improvised filters to reduce the amount of moss and grit going into them. Stage 1 of the filter is some folded metal 1cm mesh, and stage 2 is a nylon sieve. These filters need cleaning out every couple of months, but it only takes a few seconds.

If the IBCs do get too much sediment in them, you could probably clear it by opening the big lever-operated outlet taps – the powerful gush of water would clear most of it I think.

When finding IBCs, another desirable feature, probably not mentioned in the original blog post, is that some have metal bases, and some have wooden bases – metal bases are preferable I think, to avoid rot in the long term (that’s why I built a proper roof over 2 of mine, to keep them dry).”

The tanks all have overflow pipes fitted on the side, close to the top, using standard plastic domestic sink waste pipe.  For completeness,  I will add a photo of those in due course.