Can Chlorine Damage Your Hot Water Cylinder?

March 1, 2019


With the recent chlorination of Christchurch’s water supply, we’ve seen a directly correlated increase in the failing of hot water cylinders in the properties we manage. Our vigilant property managers have been responding to calls from affected tenants and landlords in a swift manner to minimise interruption. Regardless of our prompt responses, a leaking hot water cylinder can do a lot of damage, so we thought we’d give you the lowdown on the chlorination issue as a whole, and let you know what signs to look out for to ensure your cylinder isn’t on the blink. 


Why was the Christchurch water supply chlorinated?

The Christchurch City Council carries out a rolling inspection of drinking water wellheads from 156 wells at 56 sites throughout the city. The inspections are completed to ensure the safety of the water supply and compliance with NZ’s Drinking Water Standards. In January 2018, engineers raised concerns that some wellheads were not sealing sufficiently (particularly during heavy rainfall), increasing the risk of surface ground water contamination. 

This saw the Canterbury Medical Officer of Health recommend the Council temporarily chlorinate the city’s water supply in an effort to prevent an outbreak of disease like that seen in Havelock North in 2016. Given opposition to chlorinating the supply, the Council agreed to have remedial work completed on all infrastructure within 12 months, at which time chlorine would be eliminated from the city’s water supplies. 


Is the chlorine causing damage to hot water cylinders?

Since the temporary chlorination of the city’s water supply in May 2018, a link has been made to an increase of mainly copper hot water cylinder failures in properties throughout Christchurch. A first-hand account of these cylinder failures has been documented by our Managing Director at First Avenue Property Management, Melissa Benge — “In the eight-month period since July 2018 we have had 20 hot water cylinders fail and require replacing. A few of the cylinders that failed were only 3-4 years old. We have also seen a considerable increase in the replacement of hot water cylinder elements. For comparison, we had only one hot water cylinder needing replacement in the eight months prior to chlorine being introduced, and that was in quite an old property.”


An investigation is launched

With further anecdotal evidence of hot water cylinder failure throughout the city, an investigation was commissioned by Superheat, a Christchurch manufacturer of hot water cylinders, and carried out by the University of Canterbury to try to establish if the chlorine was indeed the cause of the spike in cylinder failures.

The Council agreed with the report which found that the presence of chlorine in the water, along with the other factors (such as temperature, details of installation and water chemistry), had contributed to the observed pitting corrosion which was causing the failures. They similarly agree that pitting corrosion of hot water cylinders is likely to become more frequently observed as the chlorination continues. To answer questions and assist property owners, in November last year the Council published an FAQs section on its website regarding chlorine and its effect on hot water cylinders. However, the Council advised that, due to numerous factors, there would be no compensation for property owners whose cylinders failed.


Do you need to do anything about YOUR hot water cylinder if you’re a landlord?

If you are a rental property owner and we’ve advised of a hot water cylinder failure at your property, then engage a qualified plumber to investigate. If a replacement cylinder is required, it could be worthwhile considering a ceramic unit, which some plumbers recommend, as appose to a copper one.


Do you need to do anything about YOUR hot water cylinder if you’re a tenant?

If you are a tenant and have noticed any of the following lately:

1. Moisture around or near your hot water cylinder — if there is a leak you may notice a pooling of water or wet floor coverings.

2. Discoloured water or blue-green stains in sinks and baths — that’s a sure sign of corrosion that will need to be remedied. Contact your property manager promptly.

If you have any concerns or would simply like to discuss the issue in more detail, please give the friendly property management team at First Avenue a call or drop us an email so that we can investigate further.


Update as of 28/2/19: Since this post was penned, Christchurch City Council has admitted it will miss the May deadline to cease chlorination of the water supply, and said water restrictions could be on the cards to free up wells so the necessary repairs can take place.


'Hot Water Cylinder', Christchurch City Council website


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Filed under Information for tenants \ Landlord Information

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Add a comment1 Comment

Reply Ray Bennet (Author) | April 7th, 2019 at 7:36pm
Our domestic hot water cylinder was installed March 2011 after the earthquakes.March 2019 the cylinder was found to be leaking.

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