Martin Lewis shared the "rule of thumb" for those wanting to cut the cost of their water bill ahead of the price hikes in April.
The Money Saving Expert shared the insight at this year's Ideal Home Show which opened on Friday last week.
He told listeners of his talk that the "big question" for those wanting to cut their water bill was whether they should switch to a water meter.
For those with larger homes, the Money Saving Expert said they might want to consider it.
He said: "Now some of you may have had a water meter put on you by force or you moved into a property with a water meter and you have no choice, you cannot choose back.
“But for those of you who currently have water bills, you can opt to move to a water meter.
"Then you have roughly a year or two years depending on which company, to move back to water bills if it doesn't work for you.
Martin told the audience that the "rule of thumb" applied to those who had a large house with fewer people actually living there.
He added: "Say, if you have a four-bedroom house and there are three of you living there, the likelihood is you are better off on a water meter."
He explained that this is because water bills are based on the value of a person’s house, meaning that the bigger the house, the bigger the water bills will be.
Martin continued: “Of course, if you move to a water meter, then you're being measured on the water that goes in and the water that goes out – the sewerage charge goes into it as well.
“So, the fewer people you have in the house the lower your water meter will be.
"Hence the equation: big house with few people, better on a water meter, small house with lots of people, you’re better on water bills.”
The Money Saving Expert has preached this piece of money saving advice before and often urges people to use the Consumer for Water's water meter calculator to check whether they would save.
The calculator asks you questions about your water use and tells you your estimated costs if you have a meter.
These are questions like how many people live in your home, the number of showers you have a week, your dishwasher use, and what you're paying at the moment.
In April, water bills are to see the biggest increase in bills for around 20 years, with the annual bill for an average household in England and Wales hitting £448.
How much your bill is to rise exactly will be dependent on your water provider.
You can see all the water rates for where you live here.
