water authorities can insist on installing them now under certain circumstances
"Do I have to have a meter?
Your company can choose to install a meter at your property. However, it can only charge you using the meter if you:
• use an automatic watering device (such as a garden sprinkler);
• automatically fill a swimming pool;
• have a power shower or extra large bath;
• use a reverse osmosis water softening unit;
• are the new occupier of a property (provided it has not already sent you an unmetered bill); or
• live in a water stressed area where the Government has allowed compulsory metering as part of a plan to maintain secure water supplies."
https://www.ofwat.gov.uk/wp-content/uploads/2015/10/prs_lft_101117meters.pdf
the water meter or not rule of thumb is if you have got less adults in the house than bedrooms then you should save.