Plumbers in Christchurch are reporting huge spikes in the number of broken hot water cylinders after the city's water was chlorinated in March.
Chris Rankin, the managing director of The Cylinder Guy, said Havelock North residents had experienced the same situation when their water was chlorinated.
"It's pretty concerning as some people cannot afford to pay for a replacement cylinder so suddenly."
Plumber Darren Chatwin said he was replacing four times as many hot water cylinders since the city's water was chlorinated.
He said the high level of chlorine in the water was corroding the copper pipes in the hot water cylinders, causing leaks and breakages.
The Christchurch City Council said it was aware of the potential impact chlorine had on reducing the pH of the water making it more corrosive.
Johnny Gardner, of Inline Plumbing, said he had both sold and replaced more cylinders than usual in the last three or four months.
He believed the cylinders were leaking internally.
"Elements are eating into those products."
Gardner said the situation could prove expensive for homeowners.
"We, all of a sudden, have chlorinated water and we're now having all of these issues."
Many Christchurch residents have complained on Facebook forums that they've had to replace hot water cylinders that have been installed as recently as 18 months ago.
A homeowner, who did not want to be named, said his hot water cylinder had just failed, after only 18-month-old of use.