Te Mato Vai Disinfection: Chlorination

Chlorine powder saftey warnings.

Te Mato Vai Disinfection: Chlorination.
Compiled by: Andy Kirkwood, Justine Flanagan, 2019.

Contact: [firstName] @ islandbooth.com.

Masthead Chlorine powder personal protection equipment (PPE)
Source Principles and Practices of Drinking-Water Chlorination. WHO, 2017.


This is a working draft. Final proofing in progress. Published 3 July 2019. Updated 7 May 2020.


The Te Mato Vai Project to update Rarotonga’s intakes and water main includes Stage 4: Water Disinfection to kill or inactivate micro-organisms.

Public Response: No, No, Kare

The public response to adding chlorine to the water supply was first canvassed in a household survey in 2008 (reported in the 2009 ADB Report), with similar responses preferring non-chlorinated disinfection at public meetings in 2014.

Chlorination was again presented by the Te Mato Vai Project Management Unit as the recommended disinfection option at Disinfection Presentations in 2019. The response from the public was again ‘no’.

Government / Ministry of Health / Te Mato Vai PMU / GHD response has been to cite international drinking water standards and defer to the recommendations of the offshore consultants commissioned to research, plan and specify the infrastructure project.


What is Chlorine Disinfection?

Chlorine disinfection is achieved through the addition of either Sodium Hypochlorite or Calcium Hypochlorite solution to the water supply.

The exact mechanism of chlorine disinfection action is not fully known.

  • One theory is that chlorine directly destroys the bacterial cell.
  • Another theory is that chlorine inactivates the enzymes which enable the cells to use food, thus starving the organisms.

Drinking Water Plant Operator Certification Training. Module 25: Hypochlorite (2006)


ADB Report: Planning the Infrastructure Project (2009)

A Community Attitude Survey was conducted as part of the Asian Development Bank (ADB) report Preparing The Infrastructure Development Project: Cook Islands. Included in the survey were questions to gauge the willingness of households to pay for water supplies.

…a significant objection to the taste of chlorine in water (44 percent objected, 9 percent were unsure, 30 percent had no objection to it and 16 percent would accept but prefer an alternative if practical).
See: Vol. 5: Household Survey (2008 survey of 330 households in Rarotonga)

The authoring consultant interpreted the above survey results to be in favour of chlorine disinfection at 46% (30% + 16% ‘if no other alternative’), however it is equally–valid to conclude that 60% were opposed to chlorination (44% + 16% ‘would prefer an alternative to chlorine’).


Te Mato Vai: Water Supply Master Plan for Rarotonga (2014)

Building on the ADB report, the Te Mato Vai Water Supply Master Plan for Rarotonga set out to:

  • identify the deficiencies in the water supply network caused by deterioration of the existing network, changes in population growth and legislation; and
  • analyse the deficiencies under current peak conditions and future peak water demand conditions, to determine appropriate solutions and associated costs.

The topic of chlorination was raised at the 2014 Te Mato Vai Community meetings. At the time Secretary of Finance Richard Neves provided assurances that:

“…there will be no centralised disinfection of the water once the [Te Mato Vai] project was completed in three years’ time.”
No Chemicals Will be put in Water. Cook Islands News, Apr 2014

However, within 2-3 weeks of Neves’ statement, a government press release and the views of the Health Secretary were published, both releases continued to present chlorination as the preferred disinfection option (although the issue of chlorination was muddied by being combined with references to fluoride).

In the closing comments of a Research Report on the … research report, a consultant from AECOM (the firm that authored the Master Plan) observed:

Although the Master Plan sets out a number of recommendations in order to meet the goal of reliable potable water, ongoing local resistance to the use of chemicals in the water, such as chlorine, may limit the effectiveness of the water treatment.


Watercare Raw Water Quality Review (2014)

In August 2014, Watercare New Zealand established a laboratory facility in Rarotonga to collect water quality data from the (then), 12 intake streams. On request from GHD, no microbial tests were conducted.

Given the highly variable turbidity it is likely that there would be a significant risk of microbial pathogens present in the water supply. Upon request from GHD Ltd microbial tests were not undertaken by Watercare Laboratory Services Ltd. As a result an assessment of compliance with DWSNZ for microbial parameters (bacteria, viruses and protozoa) cannot be made…
Te Mato Vai Project Raw Water Quality Review Rarotonga (2014). Watercare New Zealand.


Te Mato Vai Special Select Committee (2014–2016)

Initiated in Feb 2014, a petition against the Te Mato Vai Master Plan was tabled by the Opposition (Democratic Party) and presented in Parliament in April 2014, with 1946 signatures. It was subsquently referred to by the media as having attracted ‘over 2,000 signatures’.

Written in both English and Maori, the document lays out 11 points of concern outlined by the committee, including the project’s estimated $60 million cost, technical data cited by officials, and allegations of conflict of interest against elected officials.
Last Minute Bid to Halt Te Mavo Vai, Cook Islands News

Presented to Parliament in April 2014, the petition ‘failed to gain traction’, but was revived in June 2015.

Action on the petition was finally motioned in June 2016 and established the Te Mato Vai Special Select Committee. The Committee was charged with ‘considering the Grievances’ and ‘Reporting the findings and conclusions by Dec 2016’.

The Te Mato Vai Special Select Committee Report was presented to Parliament in June 2017 with the Project Management Unit’s Findings.

The Findings are the opinions and assumptions of the PMU. Findings are not evidenced or supported by formal documentation or any counter submissions made to the committee by petitioners.

Grievances 7 and 11 relate to disinfection.

GRIEVANCE 7.: That the general public has been deceived into believing that the public meeting consultations process is meaningful and potentially influential when in fact most decisions have already been made.
PMU Response (2.): Not only were concerns voiced at the consultation meetings listened to, but also changes have been made, where they have been deemed valid, to the master plan; which was re-published shortly after its adoption. In addition no land was taken by warrant, there was to be no water charges for the first 400L per person per day and charges and only for the excess usage over and above the allocation, there was a change to the composition of the PMU, the responsibility for the PMU was shifted from ICI to the Water Authority, and the idea of co-management of the water resources was introduced.

GRIEVANCE 11.: That expensive facilities to bring the water supply to potable standards are unwarranted when much of that effort would go to waste and to agriculture, especially when other options exist for delivering potable water to homes and kitchens (village filling station, commercial standalone plant, domestic u/v. subsidized units)
PMU Response (1.) This is a direct example of where the public was consulted on a range of methods to deliver potable water, and as the revised master plan shows, the option is to subsidise UV filters at the consumers end of the system. So people were listened to, not deceived.
(2.) We believe it is archaic in a modern country that people have to drive or somehow travel to public filling stations or commercial vendors to get potable water, especially as that impacts on our most vulnerable people and in particular on dependents like children and the elderly.
(3.) Another example where we have taken concerns on board is the issue of adding fluoride and disinfection with chlorine. The issue of ‘treatment’ will be separated from ‘disinfection’ in the new master plan. This will allow time to continue a dialogue about disinfection, together as community, and agree in the future how to best to define “appropriate water quality”. Investigations are ongoing to address this.

It is unclear from the Select Committee Report if the ‘new master plan’ referred to is the ‘final’ that was released in Apr 2014. If so, the Appendix to the 2014 document includes the statement:

‘Non-chlorination of potable water was discounted’

The AECOM consultant’s opinion is that chlorine disinfection would be required as part of the water treatment system in order to achieve potable water.

A further Grievance relates to water charges:

GRIEVANCE 1.: That Cook Islanders are fundamentally opposed to paying for water so any water project premised on vague and uncertain ‘user pays’ principles is unacceptable.

This Grievance acknowledges that there has been an exchange between Landowners and the government. The government has been allowed to use the land in return for providing a system to distribute water from the catchment areas.

The first seven of the eight responses from the PMU are deliberately evasive, pointing out that (when supply runs low) buying water is already paying for water; that we should just ‘get the system up and running’, and that there will be more consultation. At point eight there is an admission that ‘water may be charged on a excessive use basis’, and that ‘Commercial businesses will be charged as appropriate’. Also that sources of water for agricultural purposes are being investigated by the government (meaning NOT the PMU). Having exhausted the casual reader, detail is finally provided in in Response 7.1.12.

Potential Charges for Excessive Use of Water
7.1.12 In terms of the government‘s direction regarding domestic households there will be no charge for water for the first 400 litres per person per day but given that it will cost between $1.2 and $1.4 million per year to operate and maintain the water system if there is a level of water use that exceeds what is considered fair use for households then penalties will need to be considered for households wasting water by exceeding the free allocations of water per household. This may translate to about $30 per month for average size households (less than 4 people) and about $70 per month for large households (more than 5 people).

It is unclear how much a household with four (whole) people will be charged. The Paper was not written to be understood by a general audience. The Paper was not made available in Maori.

Sections 8. and 9. of the paper recommend that work should proceed with Stage 2 of the project. By the time of the paper work had been ongoing for three years.

As a member of the Select Committee, MP James Beer observations of the process included:

“… The petition was not answered by the Select Committee. The report to Parliament failed to address many critical issues and was intended to silence criticism.

The report sent to Parliament was not written by the committee and the views of some members were not reflected in the report.… ”


Cook Islands National Water Policy (2016)

Chlorination of the water supply is also directly mentioned in the Cook Islands National Water Policy (2016):

3.1 Ensure all persons in the Cook Islands have access to reliable, safe drinking water.

…Evidence of recent (2016) testing of all water catchment areas on Rarotonga has highlighted the need for water to be disinfected.

World Health Organisation (WHO) evidence for chlorination is compelling, and this National Water Policy proposes a robust system of water standards, monitoring, and transparent reporting that will ensure disinfection is managed properly and sustainably for the benefit of all.

The only test data made publically available by MoH for 2016 are results of tests at the village filling stations and schools.

…chlorination is indeed the best way to add chlorine to the water.

Reference to a specific disinfection method (chlorination) within a Policy document is inappropriate; as a different method might achieve the chosen drinking water quality standard.

Chlorination may be ‘compelling’ to the author(s) of the policy, however the disinfection evaluation criteria should be transparent to assist in assessing alternative methods that may not be known at the time the policy was written.

In effect, the policy concludes that chlorination is indeed the best way to add chlorine to the water.

Evidence: Water Quality Monitoring 2013-2016

In the policy, Appendix 4: Information for safe drinking water, details the WHO’s recommendation.

For Rarotonga, the WHO has specifically recommended chlorination, possibly supported with UV irradiation, as the most suitable disinfecting treatment method, taking into account local circumstances and public health objectives.

The WHO’s recommendation is made on the basis of: ‘Evidence of recent testing of all water catchment areas on Rarotonga has highlighted the need for water to be disinfected.’

In July 2019, the March and May 2019 catchment test data was released by the new water authority: To Tatou Vai.


Te Marae Ora Water Station Test Data (2016)

Water station test data from 2016 was published in Cook Islands National Water Policy (2016), and is provided below.

2. Quality of drinking water

MOH has provided analysis of the water quality testing they undertake at community water stations, and school water stations. Water samples are tested for faecal coliforms (E. coli and Enterococcus) as indicators of possible faecal contamination by warm-blooded animals.

MOH applies the World Health Organisation (WHO) standards for chlorinated or treated water at the water stations. Those standards are as follows:

  • Faecal coliform count 0/100ml
  • Total coliform count ≤ 5/100ml

MOH water quality testing Rarotonga community water stations (UV treatment) 2012-2016

Description 2013 2014 2015 2016
% samples meeting WHO standard of 0 faecal coliform count / 100ml
75% 73% 63% 63%
Number of samples meeting WHO standards of 0 faecal coliform count / 100ml
6 samples 27 samples 17 samples 36 samples
Total number of samples
8 samples 37 samples 27 samples 57 samples

Source: MOH

In both 2015 and 2016, 63 per cent of the samples met the WHO Standards of 0 FCC / 100ml. However, more than twice as many samples were taken in 2016 (57 samples) as compared with 2015 (27 samples). This makes it difficult to directly compare the results for the two years.

MOH water quality testing at the Rarotonga school water stations (UV treatment)

Description 2012 2013 2014 2015 2016
% samples meeting WHO standard of 0 faecal coliform count / 100ml
69% 69% 56% 61% 93%
Samples meeting WHO standards of 0 faecal coliform count / 100ml
33 samples 22 samples 9 samples 17 samples 40 samples
Total number of samples
48 samples 32 samples 16 samples 28 samples 43 samples

Source: MOH

In 2016, 93 per cent of the samples met the WHO Standards of 0 FCC / 100ml. This is an improvement from 2015, when 61 per cent of the samples met the standard. More samples were taken in 2016 (43 samples) than in 2015 (28 samples). This makes it difficult to directly compare the results for the two years.

Comments: To analyse this data further, more information is be needed about the frequency and location of the testing at the community and school water stations. The 2016 results of 63 per cent compliance for community water stations, and 93 per cent compliance for school water stations, are considered unsatisfactory. The status of these components of the indicator have therefore been assessed as ‘of concern’. The trend is assessed as static (no change), largely because of the difficulty in comparing across the years due to the different sample sizes.

Monitoring School water stations in Jan 2019 (UV treatment), Community Health Services director Dr Tereapii Uka commented:

“Everyone was on holiday so the filters in these water stations at these schools may be left uncleaned for a while. Once the maintenance is completed we expect these schools to supply clean drinking water.”

The latest village water station test results are now available from the Marae Ora website.


Monitoring water quality in the tropics

In 2002 the World Health Organisation published a review of the commonly used H2S (hydrogen sulphide) test for detecting possible contamination of drinking water. This is a presence-absence test. It does not provide a number/count. There are only two possible results:

  • Present: one-or-more indicator organisms (fail); or
  • Absent: no indicator organisms (pass).

The presence of one-or-more indictor organisms suggests that the water may have been contaminated by fecal matter. (The indicator organisms are usually not pathogenic - they are harmless.)

In the review of test methods, the WHO report made reference of testing in tropical locations.

…there is some evidence that coliforms possibly including E. coli can proliferate in tropical and subtropical waters. Warmer water temperatures may contribute to the growth of coliforms, thermotolerant coliforms and E. coli and the greater survival of some enteric bacteria, notably Salmonella, compared to coliforms …. For these reasons, coliforms, thermotolerant coliforms and E. coli are not ideal indicators of fecal contamination…
Evaluation of the H2S [hydrogen sulphide] Method for Detection of Fecal Contamination of Drinking Water (2002). World Health Organisation.

More sophisticated laboratory processing of water samples can derive (enumerate) a count of the numbers of indicator organisms present in the sample.

In the tropics, the oft-repeated phrase: ‘Dangerous levels of E. coli is more sensational than informational.

Just as the detection of coliforms and E. coli is not an ideal indicator, counting the number of each type of organism may not indicate a higher level of contamination.

Although it is often repeated in the media, the phrase: ‘Dangerous levels of E. coli’ is more sensational than informational. The presence of E. coli is not considered by the WHO as sufficient evidence of pathogens in the tropics. More research is required to determine the quality of the source water before making any decisions regarding disinfection for (tropical) Rarotonga.

For tropical waters/soils, where E. coli and enterococci may grow, alternative indicators such as Clostridium perfringens may be preferable.
Indicators of microbial water quality. N Ashbolt et al, World Health Organization, 2001.


Community Disinfection Presentations: May 2019

May 2019 the community of Rarotonga was invited to attend Disinfection Presentations, fronted by the Te Mato Vai Project Management Unit, To Tatou Vai and the Ministry of Health. At these presentations the CEO of the new water authority (To Tatou Vai) explained why chlorine was the preferred water disinfection option for the utility company.

Although the long-term health impacts of chlorination were not detailed, the key messages were that:

  • chlorination is used in other countries (New Zealand and Australia);
  • ‘only a small amount of chlorine’ would be added;
  • it will keep the pipes clean
  • water borne pathogens and mass-illness were a greater risk to public health (than any of the chronic health impacts of chlorine disinfection by-products); and
  • Rarotonga should learn from the (New Zealand) Havelock North outbreak.

Both at the presentations and in subsequet polls [1][2], the public response was that:

  • the Community should be consulted as part of choosing a disinfection method (and that the May 2019 events were NOT consultation);
  • disinfection was not needed (that water is muddy and not unsafe);
  • a non-chemical form of disinfection should be used (UV, ozone).

What is consultation?

  • The essence of consultation is the communication of a genuine invitation to give advice and a genuine consideration of that advice.
  • The effort made by those consulting should be genuine, not a formality; it should be a reality, not a charade.
  • Sufficient time should be allowed to enable the tendering of helpful advice and for that advice to be considered. The time need not be ample, but must be at least enough to enable the relevant purpose to be fulfilled.
  • It is implicit that the party consulted will be (or will be made) adequately informed to enable it to make an intelligent and useful response. The party obliged to consult, while quite entitled to have a working plan in mind, should listen, keep an open mind, and be willing to change and if necessary start the decision-making process afresh.
  • The parties may have quite different expectations about the extent of consultation.

Non-compliance With Notification and Consultation Procedures: SO319(2)(b) (2016), Victoria University Faculty of Law


The Big Decision

At the Disinfection Presentations, the Community were assured that no decision had been made, however responding to questions from the Opposition, the government indicated an intent to proceed with chlorine disinfection.

“if it is determined that chlorination is the safest and best way to ensure our water is clean for our people to drink and if the information is based on sound scientific facts and not social media speculation, then we will make that decision because this is a government that is not afraid of making hard decisions.”
Mark Brown, Cook Islands Party, June 2019

The criteria to be used by government to evaluate chlorine disinfection (and potential impacts) have not been disclosed to the public.

When questioned regarding how government would choose a disinfection method, the PMU’s response was:

This is for Government to decide.
TMV PMU, June 2019

The question the public are asking, is: who does the government represent, if it is not the people of Rarotonga?


Cook Islands Water Policy and Infrastructure Reports

All reports are PDFs.


World Health Organization


Working Draft. Updated: 7 May 2020.


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