Bmw 318i 1994 overheating even on idle - what do I do?

i think i have a problem with coolant flow.My bmw goes to red even on idle and soon after I start the engine and move 100 metres.coolant leaking out extensively. got it checked by mechanic who says there's a strange noise while engine's running and suspects water pump failure. can anyone tell me what to do about it? your opinions are valued. I live in melbourne, vic