Safe water on tap as Christchurch swallows its pride

Sunday, 25 March 2018

Christchurch is one of the largest cities in the world that does not need to treat its water to make it safe for drinking.

Most of the supply comes from a series of aquifers deep beneath the city and the surrounding area, water that has been underground for many years, often decades.

The treatment is being rolled out at the city's 56 pumping stations while engineers fix well heads vulnerable to contamination.

Naturally filtered by the layers of gravel that form the aquifers, it is protected from pollution on the surface and so is safe to drink without treatment.

It is a rare privilege and one that no one – residents, health officials or council authorities – takes lightly.

Mayor Lianne Dalziel, left, and Canterbury medical officer of health Alistair Humphrey are adamant that treated water will be safe to drink.

Treated water may taste of chlorine, but any unpleasant flavour should disappear if it is left to stand for a few hours.

* Chlorine taste unlikely in Christchurch's treated drinking water, council says

* Christchurch drinking water to be chlorinated for a year as councillors approve plan to keep it safe

Councillors made the decision to treat Christchurch's water supply in January after standards were tightened in the wake of the Havelock North crisis.

* Goldfish die after town supply water added to pond**

But amid a reappraisal of drinking water standards last year engineers found parts of the supply network were not up to scratch.

Residents could taste chlorine in their drinking water for up to a year from Monday while remedial work on the supply network is carried out.

So in January councillors took the difficult decision to introduce chlorination to protect residents from the small risk of contamination from dirty water.

What is the problem?

Christchurch City Council checks the security of its 156 wells and 56 pumping stations every five years under Drinking-water Standards for New Zealand regulations, using a rolling programme of assessments.

But after three people died and 5500 fell ill in the Havelock North crisis of August 2016, the council ordered an urgent review of its 108 underground wells to uncover any potential dangers to the drinking water supply.

Many below-ground well heads were found to be in disrepair and vulnerable to pollution from dirty surface groundwater, eventually triggering the decision to temporarily treat water at the city's 56 pumping stations.

Dave Adamson, the council's general manager of city services, said: 'There is potential of water pooling around the top of the well heads because there are a number that are below ground.

'The risk is that water could become contaminated, could go down the edge of the well head and into the well.'

The risk of contamination is extremely small – some of the city's wells still in operation date back to 1927 and amid constant monitoring Adamson said there has never yet been a contamination at those well heads.

He said: 'To give an idea of how small the risk is, the medical officer of health has not issued any public health warnings around anything, so he's got no real concerns about that at the moment.'

Canterbury medical officer of health Dr Alistair Humphrey is adamant there is little risk to public health, previously telling Stuff/: 'The probability of [contamination] occurring is very small but the consequences of contaminated water in Christchurch are quite serious.'

It is those consequences that authorities are desperate to avoid, hence the treatment plan.

What is being done about it?

Over the next few weeks chlorine will be introduced to the water supply at each of the city's 56 pump stations, an operation carried out on the consumer side of the pumps, known as the 'downstream' side, to save having to treat each individual well head.

A solution of sodium hypochlorite will effectively be injected into the pipe network before dissolving into the water to kill off harmful bacteria.

Treatment will be rolled out in stages across the city, starting in Brooklands, Kainga and Spencerville on Monday and then Riccarton, Halswell, Parklands, Heathcote Valley and around Lyttelton harbour in the coming weeks.

The two largest zones – the north-west, which stretches from Belfast to Yaldhurst and supplies 80,000 people, and the 255,000 people in central areas encompassing Spreydon, Cashmere and Papanui, across to Linwood, Aranui and New Brighton – will be treated last.

Adamson said: 'We will progressively go around the rest of the network, with the roll-out probably being complete by the end of April.

'People could expect chlorine in their water from Monday because there is the ability of water in the networks or zones to intermix.

'But if you are a long way away from a pump station that's getting chlorine then the chance of it getting to you is pretty minimal.'

Chlorination is likely to be in place for up to a year while engineers fix the vulnerable well heads.

Treatment is expected to progressively cease as sites are fixed one by one, meaning areas of the city are unlikely to be chlorinated for the entire 12 months of the work programme.

How does chlorination work – and will I taste it?

Chlorine kills the bacteria that can get into water supplies and spread disease.

The solution reacts with organic matter and in the process gives off a chlorine taste. It is a preventative measure, so if there's anything 'bad' in the pipe network it will react with it and kill it. But if there is nothing for it to target the chlorine stays in its form and remains tasteless.

'Chlorine might be noticeable at the beginning of the treatment because it does react with any organic matter in the network or even on the end of your tap,' Adamson said.

'If you look at the end of your tap, if you wiped it with a dishcloth it may well come up black.

'That is organic matter that grows in a damp environment. So there is a chance when we first turn it on that you will get a taste – the organic matter reacting with the chlorine.

'However, over a very short period of time the chlorine will kill that organic matter and the taste will disappear. If there's no organic matter present you don't get the chlorine taste.'

So there is a win-win situation for residents in terms of safety – if people cannot taste anything then there has been nothing for the solution to react with, and if they can then it means the treatment has done its job.

The taste of chlorine may be noticeable at the beginning of the treatment process but will dissipate over time because of the low dosage.

Residents in the hill suburbs may find it takes up to a week for chlorine to flush through the network as their water supply comes from reservoirs. Others should expect the chlorine to dissipate in less than three days.

But there are things people can do if they are worried about it.

Running a tap will flush through any organic matter that chlorine has reacted with in household pipework, and leaving a jug of water in the fridge overnight will help get rid of the taste.

Richard Hartshorn, professor of chemistry at the University of Canterbury, said doing so allows the chlorine to effectively evaporate as it is released from the water.

'But you don't want to leave a lid on it. If you were to fill a jug up and put Glad Wrap over the top or a lid on it then there won't be much atmosphere above and it won't be moving away, so you won't lose any of the chlorine – it will still be there.'

How fast it evaporates depends on the shape of the jug or bottle.

'If you've got a narrow-necked bottle that you've filled up there's only a very small surface area, which slows the rate in which the chlorine exchanges out.

'An open-topped jug which is much wider is better than something like a wine bottle.'

People may also notice the smell of chlorine when showering or washing because the chemical reacts with organic matter on the body.

But Adamson is certain most of us will barely notice a difference.

The council recently temporarily chlorinated water in Halswell because of an E.Coli outbreak and similar treatment was also carried out in Sockburn.

Adamson said: 'We didn't get one complaint of odour or taste, and this should be no different.

'I honestly believe that the majority of people will taste or smell nothing different, and that really is from our experience of temporary chlorination which has been on and off across the city when we get transgressions.'

Health and safety

Chlorine has been used across the world for around 120 years to make sure water is safe to drink, protecting billions of people from waterborne illness.

The Journal of the National Cancer Institute regards water chlorination as 'one of the major disease prevention achievements of the 20th century', and the World Health Organisation (WHO) says it is the most affordable and most commonly-used drinking water disinfectant, effective against more than 99 per cent of intestinal bacteria and viruses.

Studies decades ago raised the possibility of a link between chlorine and cancer, but the International Agency for Cancer Research does not believe chlorinated water is a possible cause of the disease.

Around 82 per cent of drinking water in New Zealand is chlorinated, from supplies in Auckland and Wellington to Dunedin and Invercargill – Christchurch is by far the largest unchlorinated community in the country.

Levels of chlorine being introduced to Christchurch's network are minuscule, around 0.2 to 0.5mg per litre, which is between 10 and 20 times less than the 5mg/l maximum acceptable level allowed under WHO guidelines and significantly lower than that used for swimming pools.

The Ministry of Health also says no side-effects have been found from long-term exposure to chlorine in drinking water and dismissed studies linking it to cancer as having insufficient data to show the levels required to cause such risks.

A spokeswoman said: 'The ministry considers that the benefits of chlorination and the protection of consumers from the harm caused by drinking water contaminated with bacteria far outweigh any risk associated with chlorination using the recommended quantities.'

Chlorinated water can be dangerous to those undergoing dialysis, and the Canterbury District Health Board has bought carbon filters to protect patients having treatment, being used both in hospitals and people's homes.

Fish owners are urged to either fill outdoor ponds with drums of water that have been left for 24 hours to allow chlorine to evaporate or turn down the water supply to a trickle to dilute the chemical to safe levels.

Those with indoor tanks and bowls should also allow water to sit before replacing it, the council suggested, or buy de-chlorination kits from pet shops.

Anyone still concerned can buy granular activated carbon filters to get rid of the chlorine taste.

So what happens next?

The temporary chlorination is expected to cost $600,000 to set up and about $250,000 a year to run.

While that programme is currently running to budget it is a different story for the bill for fixing the well heads.

It was originally thought just 28 wells required work, costing $840,000, but 103 have been found to be sub-standard. Engineers are still assessing the viability of many so the final bill remains some way off.

Adamson said a report due to be presented at a council committee meeting on April 11 should have a detailed project plan that is likely to include the final cost.