Now I've used it elsewhere in the garden and I've never really had any problem with it except it is inclined to make the water very alkaline because the chippings that are quite often used on a flat roof and they've got a very high P H and therefore you've got to be aware that the water that comes off is not likely to be soft it's more likely to be fair fairly hard but for reasonably tough plants I don't think I would waste it, especially in times of water shortage.