Chlorine is likely to be to blame for the failure of some hot water cylinders in Christchurch, according to a report issued by a University of Canterbury scientist.
The analysis was performed by Professor Milo Kral on four hot water cylinders, from three different brands, that had suffered corrosion 'pitting'.
The report, commissioned by hot water cylinder manufacturer Superheat, concluded that the pitting was "most likely due to the presence of chlorine" that had reacted with iron in sediments at the bottom of the cylinders.
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It could also have been affected by temperature, details of installation and other aspects of water chemistry.
The industry has seen a massive increase in hot water cylinder failures since chlorine was introduced into the city's water supply, with some plumbers reporting a 400 percent increase in work.
Manufacturers have doubled production and one property developer reported 25 failures across their portfolio.
Dr Kral concluded that "due to changes in chlorination", pitting corrosion of copper hot water cylinders was "likely to become more frequently observed in Christchurch and the average life of cylinders will be reduced.
He also concluded that pitting in copper pipes will become more frequent and potentially even more damaging as leaks behind walls and within floors can cause other kinds of damage.
Even if the chlorine treatments were stopped, the damage may already be done, he wrote.
Manufacturers Superheat said in a statement that over 2000 copper hot water cylinders have been replaced across Christchurch above the normal rate of failure in four months, from June to September.
"In the absence of a credible alternative proposition, the chlorination of the Christchurch water supply by the Christchurch City Council has caused the failure of copper hot water cylinders."
The Christchurch City Council has been approached for comment.