Rattling water pump.

I have a rattling noise coming from the drivers side of my engine which I think is coming from the water pump. Engine is the 1.4 petrol on a 62 plate Octavia. The low level water/temperature warning light came on and I've lost about 250ml of coolant so it maybe leaking from the pump. Any way any one know how difficult or easy it is to replace the pump or is the rattle some thing else? Thanks.