Without knowing all the facts about your property, old "ratable value" on which water charge is levied, your pattern of water useage it is diffficult to say. In this area Southern Water provide a rough guide on their website, see link, maybe your water authority does too?
https://www.southernwater.co.uk/Dome...YouBenefit.asp
That said, having been brought up in an area where waters meters were fitted at domestic premises as standard for many years,they make people far more aware of water usage and reduce wastage and I believe should be fitted as standard as for other utilities like electricity and gas.
Interestingly several years ago on moving with a family of 5 from from a 4 bed house in a metered area to a 4 bed house in an unmetered area I actually paid more for my annual water bills. Recently had a meter fitted in my current house my annual bill for first year is approximately 60% of the of the previous unmetered year!
When my son lived alone in a 2 bed flat after a meter was fitted he paid less than 30% of unmetered charges for the year, in fact because he'd just paid his half year water charge up-front he was in credit for well over a year after the meter was fitted.