The statute, in the order it actually works
Start with the protection, because it exists and most people do not know it does. Section 144B of the Water Industry Act 1991 is headed "Restriction on undertakers' power to require fixing of charges by reference to volume". It says that where water is supplied to premises in which a person has their home, where charges have previously been fixed without reference to volume, and where "such conditions as may be prescribed are satisfied", the company may not begin charging by volume unless the consumer has served a measured charges notice, has consented, or there has been a change in the occupation of the premises.
So the whole question is what the prescribed conditions are. They are in regulation 2 of the Water Industry (Prescribed Conditions) Regulations 1999. The list covers premises not used principally for something other than a home, and water not used for unattended garden watering, for automatically refilling a pond or pool over 10,000 litres, in a bath over 230 litres, in certain shower units, or in a reverse osmosis unit. Then the last one, regulation 2(c): the premises are not in an area determined by the Secretary of State to be an area of water scarcity under regulation 3.
Read that carefully, because the logic inverts. The protection in section 144B only bites when all the prescribed conditions are satisfied. If your home sits in a determined area of water scarcity, condition (c) is not satisfied, the restriction does not apply, and the company may fix your charges by volume without asking you. There is no opt-out drafted into it, because the protection simply never engaged.
Regulation 3 is the machinery. The Secretary of State may, on the application of a water undertaker, determine an area to be an area of water scarcity having regard to the likely demand for water over the following ten years, the water resources available or that could be made available to meet it, and the measures the undertaker could take to meet or manage that demand.
How London got determined
The current determination is the Environment Agency's Water stressed areas: final classification 2021, dated 1 July 2021. The Secretary of State accepted the Agency's advice and determined those areas on that date, following consultation in February and March 2021.
Thames Water appears in the list of companies determined to be in areas of serious water stress in 2013 that remain so, alongside Affinity Water, Anglian Water's East Anglia area, Essex and Suffolk Water, SES Water, South East Water and Southern Water. Seven further company areas were added in 2021.
The Agency is unusually direct about what the determination is for: "The determination is solely to inform whether water companies should be able to consider the option of charging by metered volume for all customers. This is known as compulsory metering. It must be considered alongside other options to manage water supplies in their water resources management plans." It also notes the one other use — that local authorities can use it to decide whether to require the tighter standard of 110 litres per head per day in new developments — and says it must not be used for anything else. It explicitly does not mean there will not be enough water, and does not reflect water company performance.
Thames Water's own summary is one sentence: "The Water Industry Act 1991 enables us to meter properties in water-stressed areas."
The programme, in their numbers
Thames Water say they are "fitting free water meters for all customers", that around 2 million customers are already metered, that they plan to install 78,000 meters this year, and that by 2030 most customers will have a smart meter. Their wider investment description puts it at over one million smart meters across the current five-year period. In London, Swindon, Guildford and Waverley the meter fitted is a smart one that sends readings automatically; some meters installed are not yet fully smart and are read every six months.
They aim to fit outside in the pavement, after a survey and once they have permission from the local highway authority, and say you do not need to be in. Where the meter has to go inside, it is an arranged appointment of about an hour.
The ninety days before anything counts
This is the part nobody reads and everybody should. In their words: "Once we've fitted your meter, we'll check remotely for leaks before activating it. This normally happens within 90 days but may take longer. When the meter is activated, your one-year comparison period will start. You won't be switched to a metered bill until after this time has passed."
During that year they send updates on how much water you are using, what future bills could be, and advice if the metered bill looks like it would cost more. You can switch early if metered charges look cheaper, and they say they will credit the account with what you would have saved from the activation date. After one year, if you have not switched, they move you over: a final unmeasured bill, then a first metered bill six months later.
So the first thing a new meter does is look for a leak, and the bill that eventually lands is built on a comparison year of your real consumption. Both of those matter enormously if you are leaking.
What happens when the meter finds one
An unmetered household that has been losing water into the ground for years has never paid a penny for it. The meter is the first moment that loss has a price, and two things happen at once.
The first is the clock. Once a leak on your side of the boundary is identified or notified, Thames Water's published position is that it must be fixed within four weeks, backed by their powers under section 75 of the Water Industry Act 1991. The notice regime and its deadlines are set out in full elsewhere on this site, including the statutory seven-day minimum that sits under the four-week policy.
The second is quieter and costs more. Your comparison year is being measured while the leak runs. Every "what your future bills could be" projection you receive is a projection of your usage plus your leak. If you fix it in month two, the rest of the year re-bases and the numbers mean something. If you do not, you spend a year being told your household is expensive when in fact your front garden is.
There is also an allowance for the water lost, with conditions attached — repair inside four weeks, evidence of the repair, a claim within three months, and an explicit exclusion where the leak was fixed under section 75. The evidence an allowance claim needs covers that properly; the reason to mention it here is timing. The allowance rewards moving quickly, and the meter has just told you to.
One thing that does not change
A meter in the footpath outside your house does not move the boundary. Thames Water's own position is that the meter is their apparatus and that the position of the meter does not determine pipe ownership or responsibility. What decides who pays is the outside stop valve and the property line, not the box in the pavement. The boundary, drawn properly is worth five minutes before you agree to anything.
Can you refuse, or go back?
CCW, the statutory consumer body, put the general rule plainly: water companies install meters for free "and you can switch back to the unmetered charge within two years if you're unhappy with the change (except for customers of in areas of England where compulsory metering is introduced)". London is one of those areas, so the trial-and-revert right most of England has does not apply here. CCW also record that 60% of households in England and Wales have a water meter and 14% have a smart one, with a goal of 65% on smart meters by 2050.
When not to call us
If a meter has just been fitted and nothing has been said about a leak, wait. The remote check runs before activation and you will hear if it finds something. If your metered bill looks high but the meter is static with the internal stop valve closed, the loss is inside the house and often visible — a leaking loo, a running overflow, a cylinder. If you rent, the repair is your landlord's. And if what you actually want is help paying, ask Thames Water about WaterSure and WaterHelp before you pay anybody to investigate.
Call us when the meter has confirmed water leaving and nobody can say where. £150 per hour agreed before we attend, no find no fee on the detection, and we repair the pipe and reinstate what was opened rather than handing you a report. Water leak repair is the whole job, not the first half.
