Hampshire window cleaning, how much water do you use a month? We are in the same area and my household and business bill is about the same as yours.
I have used 52 cu mtrs in six months for the business, so at 1 pure to 4 waste that's about 13,000 of pure or just over 2000 litres a month.
You can get a rebate form from the water board for non return to sewer.