London (change)
17 messages
20/02/2014 at 10:07

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?

20/02/2014 at 10:15

Is the roof bitumen coated?

20/02/2014 at 10:19

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.

20/02/2014 at 10:54

Have you connected it to the bath overflow pipe instead of the rainwater pipe.

Sorry Dove i could not resist. I will get my coat.

20/02/2014 at 11:13


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?



20/02/2014 at 11:46

The plastic gutters and butts may have traces of mould release agents. (Waxy silicones?) Those might cause a certain amount of foaminess when brand new.The water in the tanks gets brown from dust and leaves, and in warm weather it gets a bit bubbly from fermentation. It should not harm your plants. 

You can try putting old stockings over the end of the pipe to trap any silt and leaves.

You can also fill a stocking with charcoal and hang it from the lid into the water (do you have a lid?) this will filter any algae and keep the water fresher for longer. 

20/02/2014 at 11:57

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  

20/02/2014 at 12:46

I really wish i had not looked this topic up as it is starting to creep me out and it is sure worrying to read about. There are some types of roof cover that are less suitable for rainwater collection because they are more likely to affect the water quality:

This from Environment Agency Harvesting rainwater for domestic uses:

• bitumen felt or coated roofs can lead to discolouration and odour problems;

The general consensus, from other sites is that there is too much chance of petroleum residue and therefore should only be used on flowers and not the veg patch.

20/02/2014 at 12:52

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 

20/02/2014 at 12:53

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 

20/02/2014 at 13:19

Mother nature works in mysterious ways. She will have a good reason for this layout.

20/02/2014 at 13:41

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

20/02/2014 at 13:45

Can i request some drier weather then please. You really have been mucking about a lot lately.

20/02/2014 at 13:47

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 

20/02/2014 at 13:51

No belief needed as the evidence is everywhere. You have been my religion for many years.

20/02/2014 at 14:03

You may have pie


14/03/2014 at 13:28

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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