I have two large water butts fed off the hose roof . They have been there for three or four years with no problems but now i find that they have tiny red worms in them that come out through the tap when I use the water. Can anyone advise e if they are harmful at all. I am using the water on containers of flowers and fruit and veg, also my acer trees. If they are harmful , does anyone have any advice how to get rid of them, preferably without using chemicals if possible. If they are not harmful I dont mind just leaving them alone.

They sound like bloodworms, which are midge larvae. They're harmless.

ETA: Link (http://www.naturegrid.org.uk/biodiversity/invert/midges.html). And another (http://news.bbc.co.uk/1/hi/scotland/glasgow_and_west/6988417.stm).

Yes it sounds like blood worm

if you have fish, they'd love em!