Millions of households are being forced to have smart meters that monitor water usage by the hour.
Thames Water is telling families they must have a digital meter installed which can snoop on exactly how much water they use and when they use it.
It is feared the firm, which has nine million customers, could use this data to spy on households and introduce more expensive tariffs for those who use more water during droughts.
Thames Water are considering installing smart water meters across their network
Thames Water are considering introducing 'smart meters' to 9 million homes across the capital
The water meters work in much the same way as the digital electricity and gas smart meters currently being installed across Britain.
They send readings to the supplier every hour. This is expected to hike prices for large families, as unmetered bills are calculated based on the property rather than the number of occupants, but could save money for those who live alone.
Last night experts raised privacy concerns about the scheme.
Mark Todd, of comparison site Energyhelpline, said: ‘It seems rather “Big Brother” to force people into having a smart meter that monitors their water usage by the hour ... There is no way of knowing how firms might use this type of information in the future.’
He said that one of the ways companies could use this data was to track down people ignoring a hosepipe ban and fine them.
Under UK rules water