If you read the link supplied by snags you will fine a tenant does not need the landlords permission to have a water meter installed, also once the tenancy changes the meter can not be removed . You are stuck with the meter.
But as has been said in most cases the meter saves money. The house next door to ours is identical and has the same no of people in it , we pay £9.86 a week water rate but they pay less than £5 on the meter. Very nearly half price.
Water meters are on the way to being compusory now anyway it is government policy. Meters ,gas , electricity and water are the property of the supply company not the landlord or the occupier.