Martin Lewis has warned anyone living in a flat or a three-bedroom house could be paying more than they need to on bills.
People living in these homes need to make one simple change which affects their water bills. While you can't switch provider or go to a competitor for your water company, there is other ways that you can cut costs - especially those living in flats or houses with more bedrooms than people.
Speaking on the latest instalment of The Martin Lewis Money Show Live, the financial expert announced that there is a rule you can follow which can save you hundreds. One woman, who he referenced on the show, even saved over £1,000 thanks to Martin's advice.
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The consumer champion said: "Many people who live in flats can't get a water meter, it's called 'not practicable' to have a water meter fitted, in which case you can ask for an 'assessed charge'. That's where they work out how much you would pay if you were on a water meter, even though you can't have one, and you're charged that rather than the water rates."
He added: "Do you have more or the same number of people as bedrooms in your home? If the answer is no, a water meter may save you money in England and Wales.
"Two people, three bedrooms. Why would that be better on a water meter? Because water rates are based on the rateable value of your house, which is a proxy for the value of your house.
"You've got this big old house here so they'll be charging you a lot, but there's only two people here so they won't be using that much. Water meters measure your water usage and your sewage, so that will probably be cheaper.
"This can be hundreds of pounds. Now if you have a voluntary change, you usually have two years that you can switch back to water rates if a water meter isn't working for you.
"If you're disabled or you've got related medical issues that mean you need to use a lot of water or you're on benefits, speak to your energy firm. There's often, but not always, help available to you."
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