A Watford man returned from a dentist appointment on Saturday to find his car had been completely covered in human excrement.
Heavy rainfall flooded St Albans Road at about 10.45am, causing raw sewage to flow into the street.
Clive Harman, who parked his car outside the dentist's, came back to find the slurry of waste and toilet paper had been splashed all over his vehicle by passing motorists.
He said: "I was in my dentist having my tooth fixed and the receptionist was saying it smells outside and that it was pouring with rain.
"When I got outside I saw the whole pavement outside Jenny's Cafe was covered in excrement and toilet paper.
"Where it's gone into the road, the cars and buses have driven past and sprayed it over my car. My car was totally covered in excrement."
The 48-year-old suffered a stroke last year and was forced to retire from working as a builder. He had a lung removed and has been told he is at high risk of further strokes or even a heart attack.
Due to problems with his spleen, he immune system is also very low. He said that he is not physically able to clean the car himself.
Although rain has washed some of the waste off, the car remains splattered with toilet roll and a thin layer of excrement.
Mr Harman, from Longsprings, said: "Thames Water are telling me to get it cleaned and send them the bill but I haven't got the money because I'm on a very low income, I thought they'd tell me to bring it down to their yard.
"All I want is for someone to put a hose-pipe over it, I don't want a spit and polish. All I want is the excrement cleaned off.
"I had a hospital appointment this morning and I had to drive it, people are looking at my car and saying 'oh my god look at the state of that'.
"It's not just the excrement, it's the chemicals that go down the drains. What's that going to do to my paintwork?"
Amy Weiser, from Thames Water, said a CCTV investigation was needed to find out what caused the sewage blockage.
She added: "When Mr Harman contacted Thames Water he was told that we would compensate him for the cost of cleaning the waste water which splashed onto his car when the sewer backed up, he would just need to send us a copy of the receipt. We are very sorry for the disruption."