Hi,
sorry to keep harping on about it,but after careful consideration,have finally reached conclusion that it's ok to claim part of your water rates bill as a legitimate expense against tax,even flat rate with no meter.
Reason being that I popped into my local aquarium/pond shop the other day for some pond item,and happened to get chatting about what you can or cannot do with waste water from RO/DI systems, as fish people also use these systems too,and found out that its definitely NOT good to use waste water to top up ponds (no good for the fish at all) but fine for the garden,plants like all that muck apparently!
Anyway(I digress)we then got talking about using water for business purposes,and what you could or could not claim,and I suggested that I'd claim against tax if I ever got Metered,whereupon he then informed me that you can even claim against a flat rate water bill and that he already did (aquarium shops use quite a lot of water!) and that you could claim a percentage in much the same way as you can with various other utility bills. Presumably the actual percentage is something that you'ld have to discuss with the accountant though.
Interestingly he also confirmed something that I'd sort of "guestimated"myself which was that percentage wastage is somewhere around the 75-80% mark,although I realise this depends on a lot of factors,and how much you wish to refine and upgrade your system.
Mike