I have red/brown water coming from 1 tap in the house. An upstairs bathroom tub hot water tap periodically spurts out this discoloured water. I do not have a hot water heater. I have a boiler. I should mention that the tub isn't used very often and that all of the pipe In the house is copper. When this happens and you drain the tub there is a red/brown sediment left on the bottom of the tub.

The Brown water that you see is colored by rust. The solution would be to backflush the boiler. Good luck, Tom