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Rainwater harvesting tanks

I've had a question from a speaker called Claire Chapman. She's asked if we ever use pre-moulded plastic rainwater storage tanks, or do we always use concrete ones? If we usually use concrete ones, can you let me know why? Are they more sustainable and environmentally friendly?

Thank you! Hannah

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Hi Hannah,

My first thought re concrete versus pre moulded plastic is that concrete is widely available and can be made in small batches to suit purpose and for many purposes requiring a little knowledge and skill regarding mixing, proper placement, and curing. Pre moulded plastic is a specific skill with specific equipment and suppliers may be difficult to source or there could be delivery issues. Relative durability could also be an issue.

I speak as someone who has dealt with a lot of concrete and very little plastic so I could be biased! It would be good to hear from someone with more experience with plastic

Hope this helps! Pauline RedR

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The use of plastic plastic tanks for rainwater harvesting is becoming increasingly common as rotational moulding factories become more common, resulting in the cost of feedstocks decreasing. In East Africa you have kentainers in Nairobi, Rototanks in Uganda, and the name of the factory in Addis Ababa escapes me.

Plastic tanks have the advantage of being cheap and relatively easy to transport and install.

The plastic is generally not UV stabilised, so can be serviceable for 2 to 5 years unless a shade is provided. I would think that the costs of plastic would be similar to those of ferro cement. I have used both. Ferro cement has a tendency to creep, and once cracked is difficult to repair.

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From my little experience I agree with John: the costs are in the same range, rather in favour of cement tanks. I built cement tanks in Burkina Faso and used a PVC tank in Mali, both with a capacity of 5000 liters. Unshaded black PVC tanks will accumulate heat and the water will warm-up quite significantly during the day time whereas the water in cement tanks will stay fresh. Of course a cement tank is environmetally more friendly, consider also their respective life times. Our PVC tank in Mali is in service, but our cement tanks in Burkina are leaking and we are at this very moment trying to find out how to get them repaired... Julien Smets

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Hi Julien, I have done quite a lot of rehabilitation of leaking concrete tanks and always found the SIKALITE powder based admixture product to be very effective - mix with strong cement and brush/stipple on to a damp surface then cure it properly for at least 3 days. As I recall a couple of layers are used. My work was in sub-Saharan Africa though so I don't know what is available in Burkina.
https://www.youtube.com/watch?v=GB2xs... and http://autospec.co.za/productmedia/si... may help.

Steve Barker gravatar imageSteve Barker ( 2015-06-27 11:14:34 +0000 )edit
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Hi Hannah, in my experience it all comes down to availability and cost. Other considerations, such as how it is going to be installed, available skills, environmental considerations, etc. should come into play, but this is often not the case. I personally prefer concrete for all the mentioned reasons, including the development of local building skills. Best, 'nando

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We hosted a great webinar at the end of last year on the basics of roofwater harvesting, by Dr Terry Thomas at Warwick University with some really useful tips and guides: https://vimeo.com/113486462

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Have a look at this document that gives good recommendations how to avoid cracks: http://www2.warwick.ac.uk/fac/sci/eng...

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