Britain’s largest water company has reportedly installed smart water meters in some households without their knowledge.

According to The Sunday Telegraph, Thames Water can install some of these smart meters without notifying residents because of a rule that defined some of London, Guildford and Swindon as “water-stressed” areas.

The alleged practice means that Thames Water customers have no other alternative to remaining on a lower unmetered rate.

More specifically, the South East of England is a water-stressed region and Thames Water has legal powers to fit water meters at all properties in its region.

Under current legislation, consumers cannot refuse a smart meter – however, the company said it “always assesses the suitability of a meter for each property”.

A Thames Water spokesperson told ELN: “We are currently rolling-out smart meters in London, Guildford and Swindon. We’re seven years into our smart metering journey, with the technology playing a critical role in addressing leaks, reducing water consumption and making our water network more resilient in the face of a growing population and climate change.

“We continue to invest and expand our smart meter rollout and we’re fast approaching 1 million today, expanding to, 1.1 million by 2025, 2 million by 2030 and 2.8 million by 2035. This includes 16,000 devices this year alone which have saved enough water to fill 250 hot tubs.

“Smart meters incentivise customers to use water wisely, as they will only be charged for the water they use. They also help us to tackle customer side leaks, protecting water supplies in the process.

“Whilst we don’t need permission to fit smart meters, they are the fairest option for customers, as people only pay for the water they use. On average metered customers tend to use 12% less water.”

ELN has approached Ofwat for comment.