Seems a bit bogus to me.
We were paying £700 a year for our cottage. 2 bedrooms but the 2nd downstairs reception was previously used as a bedroom, now it’s my office. 3 adults live here and we have a small garden.
Water supply is oddly linked in with the landlords farmhouse next door and they don’t have a stop cock (have to turn the water off in the road) which also shuts ours off and our stop cock is hidden in the loft space above the kitchen. So putting in any meters is a bit more work than in your average house, but admittedly still not that hard.
They wanted to fit a meter so I explained the layout and they sent someone round to take a look. If I remember rightly it took 2 visits as the first guy was just a quick check and the 2nd actually went into more detail and did a brief questionnaire of our use. The landlord had reduced the size of our garden to give us more parking so as a result our garden was below a threshold he quoted but I cannot remember, they also thought the formal gardens at the front were ours but they belong to the landlords farmhouse and we just get to enjoy looking at them without having to do any gardening (win-win). We also corrected the account to show that it is only a 2 bed property, only has one bathroom (now with no bath, only a walk in shower) and we have modern a washing machine and dishwasher. As a result our bill halved which was very surprising.
Survey was free (Wessex water)
Meter would have been free
Minor complication to installation meant we stay off a meter.
Can’t really offer any help other than our water company have never tried to charge us for the above.