Selgas
Is your hot water system connected to the street water supply and if so is the outlet (hot water) supplied to your fittings and fixtures at mains pressure?
If so it could just be that the anode in your water tank has expired and the colouring you are getting maybe from the rusting interior of the tank.
Have it checked out by a suitably qualified Plumber who I am sure will easily identify the cause for you. 
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians
