Yeah I'm guessing as Boyan suggested it may be worth getting a reverse osmosis setup... can use the water in coolant mix too (and the iron ;) ).

Desertboy - cheers for the offer. Sulphuric acid is a bit more of a bitch than most acids as it's an oxidising agent. Seems many plastics just can't deal with it so you have to be quite careful about what you put in it... Not so bothered about damaging a pump, more bothered about contaminating the acid.

most DIY kits seem to just use air agitation and an aquarium pump to supply the air. We'll see whether the budget can stretch to a decent pump next month!