White or grey scale? I suspect it's a build up of calcium, which may well be the case is your water is described as 'hard' and drawn from a chalky source. Here in the UK we buy lime descaling fluid which gets poured into kettles, coffee machines, steam irons, and the like every once in a while.
I see Home Depot, for one, has a range of similar products that should do the trick; her in the UK we can pick up such products from most local supermarkets. Slainte.