I have suddenly been hit with a massive water bill for my business (scotland)?

In your last paragraph you state that the water is being paid as part of the council tax. In England water rates are separate and paid separately. We had a commercial business and shared water with an office upstairs, so we worked out roughly what they used and I billed them every quarter. I am afraid it was up to you to contact the water company when you moved in. Who has read your meter?, this was something you should have done when you moved in. Ask the company when it was last read and what the reading was. They might have estimated, so you need to check. Don't forget that business water is a far higher tariff than domestic.