Waiwhetu aquifer chlorination

A comprehensive investigation and assessment process was completed. This included detailed bore and asset assessments, review from international experts, and third party opinion from external engineering experts.

The investigations assessed the:

• condition of the bores in the Waterloo Well-field (and other asset assessments)
• the potential for contamination exposure in the Waterloo Water Treatment Plant collector main
• the potential for problematic leaks from wastewater and stormwater pipes
• whether a mistake in the sampling process had been made 
• whether the ‘shaking effects’ of the Kaikoura Earthquake was a contributing factor

Yes. Our report "Waterloo Well-field and Collector Main - Water Quality Security Report (June 2017)" summarises the status of our investigations into the condition of the Waterloo Well-field’s physical assets. As part of developing this report, we requested Griffiths Drilling (NZ) undertake an independent inspection of the Waterloo well-heads. Overall, the ‘Griffiths Report’ found that the bores are generally well maintained and are in good operational condition.

Yes. To investigate the potential effects of the Kaikoura Earthquake, Wellington Water engaged the services of two external engineering experts – Tonkin and Taylor, along with Pattle Delamore Partners (PDP). Based on their findings, and our own expertise, we do not believe that liquefaction or shaking effects were likely to have contributed to the positive E. coli results.

The potential impacts of future significant earthquakes on our water supply network should not be underestimated. Vulnerability to seismic activity reinforces the need for chlorination and UV to protect Lower Hutt’s drinking water supply from potential harm.

Mr Anthony Wilson and Professor Colin Fricker have independently reviewed our investigations. Both Mr Wilson and Professor Fricker are recognised water quality experts. Mr Wilson is a member of the Havelock North Drinking Water Inquiry’s Panel, and Professor Fricker is providing expert advice to the panel.

The comments and findings of each peer review are included in our investigations report.

Yes. It is available in related documents at the bottom of this page. 

In 2017, the decision was made by Greater Wellington Regional Council – in consultation with Hutt City Council. GWRC is the owner of the region’s bulk water supply system and is the registered bulk water supplier under the Health Act 1956. Wellington Water manages the bulk water supply on behalf of GWRC via a service level agreement.

We target residual chlorine of 0.4mg/L in the Lower Hutt network. This is below the 1.0mg/L guideline taste and odour threshold in the Drinking Water Standards, and well below the absolute maximum value of 5.0mg/L.

For supplies from unsecure water sources, the Ministry of Health's Drinking Water Standards for NZ require that there be a minimum of 0.2 milligrams of chlorine per litre of water (at pH 8.0) available everywhere within a distribution system, to provide effective disinfection. One milligram per litre is one part per million parts of water.

Chlorine breaks down when it comes into contact with the organic matter that it neutralises, so the level of free available chlorine at any point within a distribution system isn't constant over time. Our dosing levels are based on maintaining a minimum chlorine residual (free available chlorine) of around 0.4 mg/L.

Regional Public Health support the use of chlorination in the reticulation and monitoring of free available chlorine (FAC) as an additional barrier to unsafe water and early identification of potential issues.

Recognised water quality experts have peer reviewed our investigations and recommendation for chlorine and UV treatment at the Waterloo Water Treatment Plant. When discussing chlorine, Anthony Wilson has mentioned that it would be useful to dispel an urban myth about the taste and smell of chlorine.

Chlorine is not normally detectable by humans at concentrations less than 1.0 mg/L. However, what is able to be detected are the compounds formed when the chlorine reacts with organic material: ‘chloro-organics’.

When networks are not normally chlorinated, there are always some organics present in the pipes, typically as biofilms. The chlorine reacts with these and can produce detectable tastes and odours. It takes considerable time (many months and sometimes years) for the chlorine to oxidise all this material and reach equilibrium. With time, the tastes and odours that may be experienced and perceived (noting that some of these are likely to be psychosomatic) will gradually reduce.

If your water has a chlorine taste, try putting the water in a container or jug in the fridge (this helps the chlorine dissipate from the water). Boiling the water also helps take the chlorine taste out of the water.

You may find that using a water filter that uses carbon filtration helps. Please consult the manufacturer's instructions on recommended use.

The Waterloo Water Treatment Plant normally supplies drinking water to about 155,000 customers per day on average. Of these, about 74,000 customers located in Lower Hutt received unchlorinated drinking water up to April 2017. The remaining 81,000 customers located in Wellington city have received chlorinated water since the early 1980s.

The process of chlorinating the drinking water supply to Wellington city occurs at the Gear Island Water Treatment Plant, where it is also 'topped' up with chlorinated drinking water from the Wainuiomata Water Treatment Plant to ensure a sufficient amount of drinking water reaches Wellington City on a daily basis.

Public health issues demand action. There were no acceptable alternative courses of action.

Up until late 2016, bores in the Waterloo Wellfield were considered to be secure. The rising bacterial trend and E.coli detections indicated that a change had occurred. 

Wellington local body authorities have considered the issue of chlorination before. Since the 1980s, the decision to supply unchlorinated water has been considered by both Hutt City Council and Greater Wellington Regional Council at various times. In 1996, GWRC undertook an assessment of the risks of supplying unchlorinated water, and considered on balance that water to be supplied by the Waterloo Water Treatment Plant should be chlorinated. At the time, the final decision to chlorinate was made by HCC, who ultimately elected not to proceed with chlorination. The matter was considered again in 2003, and the decision not to chlorinate remained in place.

In 2017, the decision for ongoing treatment to manage the risk of potentially harmful organisms in drinking water supplied at the Waterloo Water Treatment Plant was made by Greater Wellington Regional Council – in consultation with Hutt City Council. The regional council is the owner of the region’s bulk water supply system and is the bulk water supplier under the Health Act 1956. Wellington Water manages the bulk water supply on behalf of the regional council via a service level agreement.

Corrosion of metallic fittings used in conveying or storing water (including copper hot water cylinders) can be caused by many factors – including the quality of manufacture and composition of the material, soil type (when underground) and water chemistry.

Wellington Water uses treatment processes to minimise corrosion caused by water quality as reflected in the pH and alkalinity of the water that leaves the treatment plant. However, because of the complexity of metal corrosion mechanisms it cannot guarantee elimination of corrosion of pipes, pipe fittings and storage vessels.

Chlorination is the most widely used method of water supply network disinfection in the world, and its levels are closely monitored to be within the limits recommended in water quality standards. It provides a critical water safety barrier to ensure customers who are connected to the water supply network are protected from illness should contamination of the water ever occur.

After a period of hot dry weather (like the summer in 2017/18) there can be an increase in leaks being reported. This is due to a number of factors including:

- the promotion of garden watering restrictions increased public awareness about water conservation and encouraged behavioral change, such as reporting water leaks to conserve water
- the possible impact of changes to conditions, including ground conditions and water treatment
- an increase in leakage due to normal wear and tear / corrosion over time

We introduced chlorination to previously untreated supply from April 2017. While this coincides with the increase in leakage over the 2017/18 summer, it cannot be said that one caused the other. This is supported by the wide distribution of the increase in leaks reported – as they also came from areas where chlorination has been in place for decades.

The Drinking Water Standards NZ recognise three classes of microorganisms that may cause disease: bacteria, viruses, and protozoa.

UV treatment manages the protozoa risk, whereas chlorine on its own only manages bacteriological and viral risks.

Yes. At the Buick Street and Dowse Square public fountains. The water is now subject to on-site filtration and UV treatment. Our information sheet "No chlorine at public fountains" is available below, under related documents. 

The drinking water supply was continuously chlorinated from April 2017. As well as for three-day periods in December 2016, and February 2017. 

There was no evidence that the contamination detected in the supply was associated with any increased level of illness in the community.

Drinking water across Wellington complies with the Drinking Water Standards New Zealand. We work closely with Regional Public Health’s Drinking Water Assessors to ensure our monitoring and oversight of the Wellington region’s drinking water supply manages public health risk.

Historically, 'secure' status has been assigned to the eight bores in the Waterloo Wellfield. The secure status relates to the bores, and not the aquifer.

Although artesian water had been considered as being 'pure' it comes from a dynamic environment, so it requires rigorous and regular monitoring. We need to act on trends in any monitoring results, or following significant events that may impact on the aquifer (eg earthquake).

The key factor in 2017 is that there are indications of changes in the source water that now need to be managed with treatment to provide an appropriate level of assurance regarding water quality and safety. The security status of the wells is a technical aspect that should not detract from what is appropriate management to maintain water safety and quality. The proposed treatment options of both chlorine and UV are likely to meet the DWSNZ whether or not the wellfield is classified as secure or non-secure. 

Current studies indicate that using or drinking water with small amounts of chlorine does not cause harmful health effects. Its widespread use has been a major factor in reducing illness from waterborne diseases.

If you feel your skin getting dry or ‘itchy’ use moisturiser after having a shower or bath. If you notice increased skin irritation, asthma symptoms or other symptoms – seek medical advice. Even with the small volumes of chlorine used, some people will be able to taste it and some will notice the smell.

Yes, in a small number of people chlorine can be an irritant for an existing condition such as asthma or eczema. If you notice increased skin irritation, asthma symptoms or other symptoms - seek medical advice. You can contact Heathline 24/7 free on 0800 611 116 or your family doctor (GP).

Increasing total coliforms have been recorded at raised levels since September 2016. Since January the levels of total coliforms give evidence of a concerning trend.

Coliforms are not a health threat in themselves, but they can indicate if other harmful bacteria are present.

The most significant change in water quality is three detections of E.coli between December 2016 and April 2017. Collectively, the trend in coliforms and E.coli are evidence that water quality was contaminated.

Total coliforms refer to a group of 16 different types of bacteria. These bacteria are found in soil, vegetation, animal waste, and human sewage, and many are not harmful.

The outbreak of gastroenteritis event in Havelock North in late 2016 demonstrated the risks associated with supplying drinking water from an aquifer. Wellington Water undertook a ‘lessons learnt’ review of the unchlorinated water system following the Havelock North incident. 

Historically, Wellington Water has undertaken sampling every second day from a ‘sampling point’ on the Waterloo Water Treatment Plant collector main. From early September 2016, as a consequence of the lessons learnt review, the sampling was increased to daily. In addition, the sampling method for E.coli and total coliforms was changed from a presence/absence method to the enumerated method – which determines the Most Probable Number (MPN). MPN is a counting method that estimates the number of coliforms through a combination of probability tables and the number of positive reactions.

After obtaining independent specialist advice, samples to test for protozoa began from both the Waterloo collector main and Gear Island Water Treatment Plant on a fortnightly basis.

Wellington Water has a rigorous and thorough monitoring programme to ensure water is safe to drink. Daily samples are taken across the system of bores connecting the Waiwhetu Aquifer to the Waterloo Water Treatment Plant.

We work closely with Regional Public Health’s Drinking Water Assessors to ensure our monitoring and oversight of Wellington region’s drinking water supply manages public health risk.

After the first detection of E.coli from the Colin Grove bore on 1 December 2016, temporary chlorination was implemented for three days. Following the second positive E.coli test from the Naenae Reservoir on 4 February 2017, temporary chlorination remained in place for three days of clear testing. Following receipt of the third E.coli result in April 2017, the decision was made to continuously treat the water supplied by the Waterloo Water Treatment Plant with chlorine.

Water samples are taken at the public fountains at Dowse Square and Buick Street every four days for E.coli, bacterial and water chemistry indicators.

The treatment solution installed at the public fountains are fitted with recording instruments that allows Wellington Water to monitor water quality, in real-time. Regular water samples are analysed by an accredited laboratory and reported directly to the Wellington Water assurance team. This activity ensures high quality water is provided.

Treatment processes at Te Marua and Wainuiomata involve “coagulation” as well as “flocculation”. Chlorine is also used as a protection measure at these plants. Explanation of the treatment processes is available here: Water Treatment

Coagulation and flocculation require physical space and equipment which is not a feasible option for the size and location of the Waterloo Water Treatment Plant.

To safeguard water supply against giardia and cryptosporidium, appropriate water treatment processes are required, such as coagulation and conventional filtration, membranes, or UV light.

With regard to the capital and operating costs associated with continuous chlorination, it is noted that Wellington Water is still undertaking detailed design.

Indicative estimates are that the capex investment to meet summer demand from Waterloo is likely to be around $5m in 2017/18. There may be additional capex costs not yet determined, which will be included in the 2018-28 long term plan for consideration e.g. building modifications at the treatment plant to house UV equipment.

Additional operational costs for 2017/18 are expected to be around $1.5m – incorporating power, chlorine, the regional water safety plan, and additional staff resources. Annual operational costs of approximately $875,000 will be ongoing from 2018/19.

The capital costs in financial year 2017/18 will be sourced from the reallocation of funding that has been set aside for establishing Wellington Water’s ‘strategic stores’ for resilience purposes – $4.6m was originally allocated to this activity. This resilience project has been deferred to the 2018/19 financial year. Accordingly, around $5m will be put forward for approval for 2018/19 to cover original resilience work.

To safeguard water supply against giardia and cryptosporidium, appropriate water treatment processes are required, such as coagulation and conventional filtration, membranes or UV light. The Drinking Water Standards NZ recognise three classes of microorganisms that may cause disease: bacteria, viruses, and protozoa. UV treatment manages the protozoa risk, whereas chlorine on its own only manages bacteriological and viral risks.

We decided to install ultra violet (UV) units to provide further protection against potentially harmful organisms in water supply. This decision was based on international best practice of utilising multiple barriers to safeguard drinking water supply. The peer review of our investigations report also advised that a combination of UV and chlorine is international best practice.

In making our recommendation to Greater Wellington Regional Council we considered a range of treatment options. This included a return to pre E.coli detection state (no chlorine), continuing to chlorinate only, UV disinfection only (no chlorine) and UV disinfection with chlorine.

Our selection of UV and chlorine was premised on ensuring that safe and healthy drinking water would continue to be provided to our Lower Hutt customers. It ensures compliance with the Drinking Water Standards NZ, and is a cost efficient option.

No. Water sourced from the Waiwhetu Aquifer is drawn from eight bores located along the “Knights Road spine” collectively known as the Waterloo Wellfield. Water is transferred to the Waterloo Water Treatment Plant via the Waterloo collector main. Four of these bores are offline due to E.coli detection or high coliforms.

The bores affected by E.coli are now "provisionally secure" which means they are placed on a 12-month intensive monitoring programme. This starts from the day it is operational which can be anytime. Wellington Water have decided to take the bores offline until the UV treatment system is up and running at Waterloo Water Treatment Plant. With chlorine added to the supply system there can be greater confidence in the quality of drinking water.

The Drinking Water Standards NZ recognise three classes of microorganisms that may cause disease: bacteria, viruses, and protozoa. UV treatment manages the protozoa risk, whereas chlorine on its own only manages bacteriological and viral risks. A combination of both treatment measures provides a multiple barrier protection system.

No. Treatment processes at these plants involve “coagulation” as well as “flocculation” to remove potentially harmful organisms. Drinking water at these plants has been chlorinated since the early 1980s.

Historically, the natural filtration processes of the Waiwhetu Aquifer has been relied upon.

After the Havelock North incident in August 2016, Wellington Water undertook a lessons learnt review of Lower Hutt’s unchlorinated water supply. The risk of protozoa was identified, and action and decisions were taken to manage the potential public health risks.

The first UV unit is expected to be operational at the Waterloo Water Treatment Plant by the end of August. A second unit will be operational by early December 2017 in order to meet the demands of drinking water in the summer. The units will be subject to a final assessment by RPH’s Drinking Water Assessors. Wellington Water’s technical expertise has considered what will be necessary to meet the validation, prior to recommendation of the treatment unit.

Every day. We sample the Waterloo bores every day for E.coli and total coliforms. We have recently installed analysers on each bore to assist with operational management.

Water samples are taken at the public drinking fountains at Dowse Square and Buick Street every four days for E.coli, bacterial and water chemistry indicators.

The treatment solution installed at the public fountains are fitted with recording instruments that allows Wellington Water to monitor water quality, in real-time. Regular water samples are analysed by an accredited laboratory and reported directly to the Wellington Water assurance team. This activity ensures high quality water is provided.

Water supplies that have no residual disinfectant are vulnerable to contamination. Chlorine residual monitoring can provide early warning of contamination in the network and provides real time insight into what is happening within the reticulation.

An additional benefit of chlorine is the control of biofilm. Biofilm is bacterial growth that occurs in unchlorinated networks which can harbour harmful bugs. Generally, biofilm development is to be avoided where possible, and maintaining a residual of chlorine helps with this. 

Wellington Water are managing the protozoa risk by daily monitoring of each individual bore for E.coli and total coliforms. The monitoring will indicate if there is faecal contamination. Where there is faecal contamination, there is higher risk of protozoa like giardia and cryptosporidium. Monitoring for protozoa is also undertaken at the at the Waterloo Water Treatment Plant and Gear Island plant inlets on a fortnightly basis.

We are currently reducing the risk of protozoa by not abstracting from bores that have shown indications of concern from laboratory analyses. These bores will be required to run during summer demand, and UV treatment will be required to safely use them.

On average, there were three positive E.coli results per year recorded in the previously unchlorinated Lower Hutt network. This compares against the chlorinated networks in the Wellington region who record between zero and one every two years.

As there is no disinfection barrier in an unchlorinated network this adds a greater risk of consuming contaminated water.

The majority of transgressions with E.coli in Wellington’s reticulation network over the last ten years have been in the unchlorinated Lower Hutt zone. A further example is within Wainuiomata, and detection of E. coli usually being associated with a switch to Waterloo water.

The decision in the past to manage this risk with increased testing carries a residual risk. As there will always be a delay identifying the presence of contamination due to the time it takes for lab detection – a high level of contamination could still lead to significant public exposure prior to identification and mitigation measures, even with daily testing. The additional protection measures to be introduced in 2017 mitigates this risk.

Yes. To protect public health the water is now subject to on-site filtration and UV treatment.

The public health risks associated with an outbreak of harmful organisms in water supply have been well demonstrated in Havelock North. We now know that relying on the Waiwhetu Aquifer’s natural filtration processes is likely to be a risk to public health.

Regional Public Health support the addition of UV treatment to the Buick Street and Dowse bores as a way of managing potential public health risk.

No. As a part of Wellington Water’s response to rising bacterial levels, and three detections of positive E.coli test results it was recommended that Hutt City Council close the water fountains at Buick Street and Dowse Square until each could be fitted with on-site filtration and UV treatment systems.

Buick Street re-opened for public use on 26 June 2017, and Dowse Square re-opened on 9 August 2017.

UV water treatment is widely used for both public and private drinking water supplies. At the flow-rate of water from the public taps, the UV units provide effective barriers against contaminants such as giardia, cryptosporidium, campylobacter and E.coli, and will comply with the Drinking Water Standards of New Zealand. 

The water from the secure bores is generally of good quality, but the reason for treatment is to further mitigate the risk of contamination.

Waterloo Wellfield Water Quality Contamination Investigations - August 2017

No chlorine at public fountains