A man was left with a £17,500 water bill after a fault with his meter left the device constantly running.
Mark Searcey, 30, was left panicked after his water company took the money without warning because of the faulty meter.
To make matters worse he was then charged an additional £4.80 for cancelling his direct debit.
Mark, who suffers from learning difficulties, diabetes and a condition called Moyamoya - which effects the flow of blood to his brain - made the discovery on October 15.
After initially laughing it off as an administrative error by Northumbrian Water , he was stunned to receive a letter from the utility company demanding the cash still be paid just four days later.
Mark, from South Shields, Tyne and Wear, who makes his water payments by a regular direct debit, said: "It just gave me a shock.
"I was checking my bank account when I noticed £17,500 had been withdrawn.
"I had to look at it again as I couldn't believe my eyes. I couldn't afford to pay that amount. There was no letter warning me about it. The money was just taken out in one go."
Mr Searcey, who has lived in his flat for two years, believes the massive figures could have been calculated due to a fault with a water meter and a leak in his back yard.
He says a Northumbrian Water worker inspected his home recently and found there was a fault with his water meter, which meant it was still running - and building up costs - even when water facilities were not being used in the house.
They also later discovered a leak under the property.
He said: "At first I thought it was a laugh, but after I contacted my bank to get the money refunded into my account I got a letter from Northumbrian Water still demanding the money be paid.
"I have a range of disabilities and health issues. This is the kind of stress I don't need. I just want it to get sorted out."
The full amount has been refunded after Mark contacted the bank and he has also cancelled his direct debit.
A Northumbrian Water spokesman said: "The issue is complicated, involving a leak at the property, estimated meter readings and difficulty in contacting the customer.
"A bill was sent in error.
"We will be visiting him to fully check his supply for leaks and his bill will be recalculated based on his average usage.
"We have agreed a payment plan with the customer for future bills and are sorry for any inconvenience."