A landlord who owns 65 rental properties in Hastings says he has had to replace 50 hot water cylinders since water in the city had chlorine added to its water.

Graeme Fowler, who owns 80 homes in total in Hawke's Bay, says he used to replace two or three cylinders a year.

But in the two and a half years of chlorination that followed the Havelock North water crisis in August 2016, he'd seen a dramatic spike in cylinder failure.

He said the cylinders he had to replace varied in age, but on average they would be between 15 and 20 years old.

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Normally cylinders cost between $1800-$2000 to replace, meaning he had spent well over $100,000 replacing them.

None of the cylinders in his 15 Napier homes have needed replacing since 2016, he said.

Fowler said he felt the council were making the best of a bad situation, describing chlorine in the water like a prescribed pill - good for you, but may come with side effects.

Plumbers have also seen an increase in leaky hot water cylinders since water chlorination in Hastings.

Tim Masters from Masters Plumbers said they had fixed or replaced dozens of hot water cylinders since 2016.

"We have noticed a spike in replacing hot water cylinders and repairs to copper pipe work."

He said chlorine breaks down calcium build-up on the inside of the hot water cylinder.

This build-up normally covers pin prick holes in the cylinder itself, so when it breaks down the cylinders leak.

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He said most of the replacements and repairs had been made in older houses in Flaxmere and Hastings, although they had also repaired some in Havelock North.

He said a carbon filter would reduce the amount of chlorine coming into a home, and could help alleviate some of the issues, but its effectiveness would vary depending on the age of filter, how often it's changed and other factors.

A spokesperson for Hastings District Council said it had only received one claim asking it to pay to replace a hot water cylinder and this was declined.

"The introduction of chlorine removed scale in pipes and hot water cylinders, which exposed failings that were masked by the scale," the spokesperson said.

"There were a number of failures over a brief period and the vast majority of these were old units that were past their use-by date.

"Manufacturer warranties on hot water cylinders are for a maximum of five years."

The council's drinking water strategy says, after the Havelock North crisis and subsequent inquiry, all ground water should be treated as not secure, and chlorination should be used as part of a multi barrier approach.

Prior to this, water was being treated at the source, but was liable to contamination as it moved through the pipes.