Thames Water have installed a smart meter in our home so, with a bit of extra background reading, I can say with a fair degree of confidence you are likely to have a Sensus 640C water meter; it's pretty much guaranteed to be a Sensus of some sort at very least. These meters have an onboard battery, and the battery state should be transmitted to TW at the same time as any readings. As with all other aspects of the meter, it's TW's responsibility to maintain it.

That said, it's debatable whether or not we have a smart meter after all. TW are well into their programme of installing meters but are behind the curve in installing the mobile data network to receive the meter reads. We've had a smart meter since mid July 2026 and as of today (12th October) they still don't have a working mast covering our area. A smart meter that can't get its signal received isn't too smart really, is it?

Posted by: @downfield

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This arrangement is often called Advanced Metering Infrastructure (AMI). Unlike one-way automatic meter reading, AMI can support two-way communication, letting the utility receive usage data and send commands or receive equipment diagnostics.

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Just for the absence of doubt, whilst AMI can support the sending of commands by a utility company to a smart meter, that meter is still just a meter. There is no solenoid onboard, so the meter is unable to affect the actual flow of water through it. Any commands it can actually fulfill are limited to what it has control over and that in practice means the management of its own electronics and any data it is storing. A water company could, conceivably, send a command telling the water meter to change the frequency of transmission or send a command telling the water meter to report back on its battery status, but a command to turn the water supply off would be like giving me a command to indulge in some time travel.

You haven't even implied any different, btw, @downfield, but I mention this here since I'm well aware of some of the urban myths circulating about smart water meters.

@downfield I wonder if the flow of water powers a mini waterwheel connected to a generator?! I am not aware of any battery swapping in 20 plus years. Toodles.

Posted by: @majordennisbloodnok

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I'm well aware of some of the urban myths

Yes indeed.  Interesting and I take your point about flow control.  It does give them a mechanism to monitor hourly usage though and so I suppose impose penalties if they can prove use of a hosepipe while banned.  But would they be able to prove you weren't just filling a series of watering cans?

@downfield You are opening a whole can of cans there!

Posted by: @downfield

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Posted by: @majordennisbloodnok

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I'm well aware of some of the urban myths

Yes indeed.  Interesting and I take your point about flow control.  It does give them a mechanism to monitor hourly usage though and so I suppose impose penalties if they can prove use of a hosepipe while banned.  But would they be able to prove you weren't just filling a series of watering cans?

Quite right. And one could take it further still. Under any of the hosepipe restriction rules, it is perfectly legitimate and allowed to refill a water butt (e.g. next to a greenhouse) from the mains and then draw water from there into watering cans or, depending on the rules in place, feed a soaker hose irrigation system. And some water butts are enormous - we're looking at installing two 1500 litre ones. Any hourly usage data could easily pick up on a period looking very much like hosepipe watering without the activity actually being improper. You've hit on a classic case of data and information being two very different things.

As for monitoring hourly usage, that's the passport to more accurate billing and therefore why we acquiesced to the mandatory installation without any complaint. Unmetered bills are artificially high in the name of a property's rateable value from a decade or more ago and metered bills force the water companies to show their workings far more openly. The problem for us, as I said before, is that whilst the meter might be capturing hourly usage the lack of a mobile data network stops that hourly data being transmitted. Smart technology made dumb again.

@majordennisbloodnok I can only think that if there is a battery contained within the meter housing, it needs to be encased in a sealed container as, with our meter being well below ground level in our front garden, it is frequently well under water (as is the whole housing) and rather inaccessible unless the reader is endowed with very long arms! For these reasons, I have doubts that the battery might have been replaced on over 20 years without us even being aware of such an activity - wouldn’t any ‘operative’ attending to change the battery be likely to alert the householder to their reason for a presence in the garden?! Regards, Toodles.

By the way, on occasions, we have seen the message ‘estimated’ against consumption figures on our water bill which, to me suggests that any ‘smart’ data is not being received by Thames Water. Toodles.

Posted by: @toodles

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@majordennisbloodnok I can only think that if there is a battery contained within the meter housing, it needs to be encased in a sealed container as, with our meter being well below ground level in our front garden, it is frequently well under water (as is the whole housing) and rather inaccessible unless the reader is endowed with very long arms! For these reasons, I have doubts that the battery might have been replaced on over 20 years without us even being aware of such an activity - wouldn’t any ‘operative’ attending to change the battery be likely to alert the householder to their reason for a presence in the garden?! Regards, Toodles.

The product page for the meter I mentioned is at https://www.sensus-international.com/en/products/640c-640mc

There, you can see the manual and datasheet showing explicitly the reference to a battery. Of course, if your meter is a different one then the power source may be different but I doubt it.

You might also want to bear in mind that whilst your home's external stopcock (and, indeed, a meter) may be in your front garden, it doesn't necessarily follow that the smart meter is in the same place. If there is somewhere in the street that only feeds your home, the water company will normally choose to fit the smart meter there since it's easier for them to do a drive-by meter read and they don't have to ask you for access to do any maintenance. As a result, I would suspect that they've installed a smart meter somewhere that makes your dumb meter obsolete.

Irrespective, a smart meter does need to have power to do any transmitting and that power will come from a battery. If you have a meter in your garden that hasn't been touched in over more than the lifetime of the battery then that meter can't be the smart meter your water company is referring to.

@majordennisbloodnok That is my thinking precisely, I suspect that the letter sent out by TW is generic and includes anyone who has any form of metering at all! As mentioned, the numeric readings are almost always submerged and I have never been able to read them anyway. The meter has a built in stop cock and a late neighbour of mine who was a plumber, fashioned a 3 foot long pole so that we could use it to turn the water supply off if ever the need arose. Within the house, we can hear a mechanical sound from the meter whenever water is moving through the supply pipe, clunketty clunketty clunk (technical term there). Until receiving this letter informing us we have a smart water meter, I have always assumed that a meter reader visited our garden twice a year - maybe not though. Regards, Toodles.

My neighbour received an email from Anglian Water saying they suspected there was a leak in the house somewhere with instructions on how to identify.  They also gave an estimate on the number of litres that was being wasted and cost.  The neighbours already knew there was a leak - toilet flush wasn’t sealing properly - they just hadn’t got around to getting it fixed.  The estimated cost spurred them on!

Yep I caught our slow leak from a £100 bill rise 8)