Nicola Evans thought water bills for her two-bedroom Oxford flat were high at £44-a-month.

But it was not until she spoke to her neighbours she discovered she was paying for all three flats in her building.

Miss Evans, 29, of North Way, Headington, then spent months trying to find out what was going on. Now Thames Water is warning people who convert houses into flats to let them know so bill blunders do not happen.

She said: "I had this big bill come through, I asked the guy next door how much he paid for his water rates and he said he didn't pay.

"When he moved in he was told the landlord covered it, but it was in my contract to pay my water. And when I contacted Thames Water they told me they had it down as a house, not three flats."

She was told the organisation had not been informed the house had been divided into three flats, so she had received the bill for all the water used. Miss Evans, who is a nursery nurse at Stepping Stones in Glanville Road and has a two-year-old son, Daniel, said: "Basically, for two years, I have been paying quite a high water bill and it turned out I was actually paying for a whole house when I live in a two-bedroom flat. I am a single mum with a young child and I don't have the money to keep paying out these high bills.

"It's quite concerning they have said this is quite common."

She claimed she called Thames Water numerous times before she got a rebate. Her account has now been credited with several hundred pounds, the money she paid out in bills that were not hers.

She does not yet know what her new bill will be - but has been told she would not need to pay for at least a year. She said: "The whole thing has been quite frustrating and annoying. There ought to be a better system in place."

Thames Water spokesman Becky Johnson said: "The owner had not phoned to tell us he had separated it into three flats - that is where the problem has come.

"We have been in touch with Miss Evans and credited her account and been in touch with the residents of the other two flats.

"It is quite a common thing when people divide up a house into flats. The message should be if somebody is renovating their home and making it into flats, they should let us know."

The flat was rented through College and County, based in St Clements. Partner Mark Crampton Smith said: "My client bought these properties in good faith, assuming it was all as it should be in terms of utility supplies.

"The first we heard about this was about a week ago. He had no idea Thames Water had not been informed there were three flats in the building."