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How to deal with bacteria in a rainwater harvesting tank

Posted by Barry Nutley on 20 May 2011 at 9:32 am

Q: I have been told that bacteria is avoided by having small ultra violet light at the top as bacteria collects on the surface

A: Yes, UV filtration will kill off any bacteria that develops in rainwater harvesting tanks (both above and below ground).

However, UV will kill everything off, so if you use the water for your garden, you will kill off all that's good about rainwater for gardens!

If you are having bacterial problems (especially in an underground tank), it is likely that contamination is coming from the roof/guttering? If may be worthwhile checking these for potential sources of bacteria. Is there a dead bird there, for example?

If you do feel the need for UV, there are many companies offering UV treatment for rainwater harvesting. Rather than recommend any company/product in particular, just Google "rainwater harvesting UV disinfection" and you will be presented with a number of options to choose from.

Photo by Pink Sherbet Photography

About the author: Barry Nutley is co-founder and director of Viridis Energie Consultants

If you have a question about anything in the above blog, please ask it in the comments section below.

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2 comments - read them below or add one


richmcComment left on: 10 January 2013 at 5:20 pm

I have RWH, with a header tank in the loft fed by a pump. I'm considering a UV system over the header tank, the system tops up the header via a pump it takes around 4 1/2 mins, a lamp on for 10 mins should do the trick, and not use too much energy.

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Combined Harvesters Ltd

Combined Harvesters LtdComment left on: 5 December 2012 at 9:46 am


It is also a valid option to have the water tested at random intervals. Either with a at home kit, or by your local water authority.  UV systems can be an expensive option. 

Jemma Tunnington


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