CDTI Grating Noise - water pump?

[DaveF]

Hope someone can advise on the most likely cause of a constant grating noise, sounding a bit like a worn pad on a disc, coming from the engine bay. It started a couple of days ago and has got louder until the auxilliary belt has now gone and the charging light is on. So either water pump, steering pump or alternator I guess? It hasn't made any squealing / high pitched noise at all, which is usually the sign of bearings failing in my experience. I understand the w/p is a pain to remove, but steering pump is quite easy? Cheers, Dave