If the cold taps in your home suffer from low water pressure and it is over 30-35 years old, chances are that it is caused by rusty, corroded galvanised wrought iron pipes. It was common practice up to the late 1970's to run cold water supply pipes in galvanized wrought iron pipes.
Melbourne's water is classed as 'soft water'. Soft water has low levels of calcium and magnesium salts which react aggressively with galvanised wrought iron pipes. Due to this process the pipe rusts from the inside out over time. This leads to lower water pressure as the inside pipe diameter is restricted more and more over time.