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I've been meaning to ask this for ages.  We've installed water butts on our downpipes - however the water in the butt which takes the run off from the flat garage roof tends to be brownish and foams when you fill the watering can.

This isn't something I've come across before.

Last summer I restricted it's use to ornamentals but was I being over cautious? What's causing the discolouration and foaming and is it ok to use on the veg patch?


All sorts of debris settles on a flat roof that doesn't settle on a pitched one. You might get an initial washing off of something from a felt type roof but in the long term they won't be washing away. Unless your roof is made of something deadly, (asbestos?) I wouldn't worry.



Nut,  not asbestos (the underneath was but we had specialists come and strip it all out and take it away in a sealed thingy).  Just bitumen-type felt roofing stuff - I suppose the brown is from the bitumen - does anyone know, does the bitumen make it foam as well?




We're fairly free from silt and leaves in the gutters and butts (although we do get rockets landing on the roof on 5th Nov).  

We did have new guttering all around last spring - but we only get the foaming in the butt that takes the water from the garage roof, not the ones on the other downpipes.

 It must be something to do with the bitumen felt - oh well, as long as there's no deadly contaminant that everyone but me knows about, I shall not worry about it.

Cheers guys  



I had a feeling I'd read or heard something, but I thought I might have been imagining it .... well, better safe than sorry then - it will continue to be used for ornamentals only then .

Cheers for doing the googling for me Edd 


A bit tedious that the flat roof waterbutt is near the veg patch and the other butts are near the flower borders - still, the exercise will continue to do me good 


I set the garden out Edd - maybe I'm Herself 


Sorreeeeeeeeeee, but what I need is a bit more deference from gardeners - it's like with Tinkerbelle in Peter Pan - you have to believe in me 

Anything thats on the flat roof, even algae spores will come contaminiate the water, leading to the discolourisation/ smell of the water. You can pop down to your garden centre, and they will have here are a couple of water purification products you can buy.

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