E. coli response for councils and water organisations
How to protect people’s health and prevent recurrent E. coli contamination in drinking water supplies managed by councils, council-controlled organisations or water service providers.
This page is designed for council suppliers and council-controlled organisations, and any organisations created as part of service delivery models developed under Local Water Done Well.
Information outlined here can help large government, commercial and community supplies respond to an E. coli detection, but make sure you understand specific responsibilities for your supply.
To understand your water supply and legal responsibilities, use the ‘What type of water supply do you provide?’ assessment tool.
Water service providers must respond when laboratory testing of treated drinking water indicates the presence of E. coli.
Take E. coli seriously
Escherichia coli (E. coli) is a bacteria often found in the gut of animals. A positive E. coli test means there is faeces from animals, birds or people in the water. When E. coli shows up in drinking water, it means a range of other harmful pathogens carried in faeces could be present too.
Anyone who drinks the water could get very sick. Children, the elderly and people with health conditions are usually at higher risk.
If E. coli is detected in treated drinking water you supply, you need to act quickly to protect people’s health, find the cause of the contamination and fix any problems.
The Water Services Authority – Taumata Arowai (the Authority) expects water service providers to respond quickly to E. coli results in line with their responsibilities under section 21 and 22 of the Water Services Act 2021.
Water Services Act 2021 – New Zealand Legislationoutbound
International best practice also promotes an immediate response to any detection of E. coli in treated drinking water.
You need to have a well-rehearsed response plan in place and be ready to act if microbiological contamination is detected in your supply. A 'find and fix' methodology should be central to this plan. Even if the exact cause of the contamination can’t be identified, you will need to find the most probable cause and remedy it.
Identify the cause (or most probable cause) of contamination
E. coli indicates that a system has failed
E. coli in treated drinking water indicates that critical controls have failed and consumers may be exposed to pathogens and become ill. Treat every detection as a high-priority operational and public health incident.
This flowchart summarises key actions and timeframes when responding to an E. coli detection. It’s a helpful summary and should be read alongside the full guidance below.
Act quickly
Immediate actions
Click the headings below for steps to take within 4 hours of receiving notification.
Urgently investigate the extent of contamination and the immediate risk to people
As well as taking further samples, you must explore the potential extent and possible causes of the contamination.
Identify how much of the water supply network could be impacted. Then focus on the affected area to complete reviews.
- Review water treatment performance data and critical control points (CCPs) for any changes or challenges to source water quality and barriers in relevant treatment plants.
- Review available distribution information for additional signs that your supply is compromised. Look at water quality parameters from the original sample point and other operational data from your supply. Consider low free available chlorine (FAC), increased turbidity, pH changes, total coliforms*, pressure fluctuations, consumer complaints, unusual water usage, backflow risks, recent work activities affecting the supply, and any additional information you can gather.
See the ‘Investigate contamination causes in depth’ section below for additional options to consider in your initial review.
Investigate contamination causes in depth
* If total coliforms without E. coli are found in a follow-up water sample, it indicates that bacteria are still present in the water. It may also indicate that treatment has not been effective or that there is a faecal contamination pathway present.
Advise the Authority within 30 minutes of receiving test results
Inform the Authority by phone 0800 454 717 or email notifications@taumataarowai.govt.nz within 30 minutes of receiving a positive E. coli result from the laboratory.
Be prepared to briefly explain your immediate actions.
Submit a full notification through formal channels (on the Hinekōrako portal) at a more suitable time. Protecting public health should be your first priority.
Your full notification will need to describe actions you have taken so far and any additional actions you plan to take. Once this is received, the Authority will notify the local Public Health Unit.
Take steps to protect public health
Decisive action is required to protect public health.
Actions should be informed by the findings of your initial investigation and may include (but are not limited to):
- increasing chlorine levels
- flushing network/pipes where and when appropriate
- isolating reservoirs or networks
- providing an alternative supply, and/or
- issuing a boil water notice.
Actions will depend on the supply arrangement and extent of contamination. Water service providers should ensure that response actions reduce risk to consumers and do not unintentionally spread contamination.
The Authority can and will intervene to protect public health if the supplier’s response does not meet the Authority’s expectations.
Issue a Boil Water notice and inform the public
You must communicate with everyone you supply water to in a transparent and timely way. The Authority expects a consumer advisory to be issued when E. coli is detected in drinking water. In most cases, a Boil Water notice is the appropriate advisory.
How to communicate that a Boil Water notice is in place depends on your supply and the people who use the water. Consider a combination of channels including:
- text message
- phone calls
- door knocking
- social media posts
- radio announcements
- electronic signage on key arterial roads.
It’s important to make sure communication reaches vulnerable populations and consumers.
Ensure that Boil Water notices or Do Not Drink notices are posted on any public taps that people might use during the incident. Our guidance and templates can help.
Issuing a drinking water notice
Boil Water notice template
This table outlines timeline expectations for issuing a consumer advisory.
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Scenario |
Expectation |
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E. coli detected in water leaving a water treatment plant indicates fundamental barriers have failed or are missing. Widespread contamination across the entire network supplied by the plant is possible.
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The Authority expects that you will issue a Boil Water notice within 2 hours. Water service providers should quickly investigate these instances and determine risk to their consumers.
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E. coli detected in, or immediately downstream of, a treated water storage reservoir must be acted on quickly. Storage reservoir may be vulnerable to contamination by animals and other pests.
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The Authority expects that you will issue a Boil Water notice within 2 hours. Isolating an affected reservoir is insufficient to protect public health due to the delay between collecting the sample, the laboratory testing the sample, and taking action following receipt of the test results.
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E. coli detected in a water distribution network may represent a localised contamination event.
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Water service providers would need additional time to undertake an initial investigation. The Authority expects you will issue a Boil Water notice within 4 hours.
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These timeframes ensure swift protection of public health. Water service providers should have response plans prepared, practised, and ready to implement.
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Issuing a Boil Water notice can have significant impacts on communities and suppliers. But the detection of E. coli means drinking water must be treated as unsafe until evidence shows otherwise. See ‘Keep the Boil Water notice in place’ in the accordion below for more information. |
Every incident is different and initial investigations may demonstrate the supply remains safe. Your investigation will inform your decision to issue and remove a Boil Water notice.
If you decide a Boil Water notice is not required, you must record how findings from your initial investigation demonstrate the drinking water is safe.
If you are unable to demonstrate the drinking water is safe, you must issue a Boil Water notice as above.
Whether or not a notice is issued, you should regularly assess the risk to consumers and consider informing them that you are investigating a contamination incident. Invite consumers to report any issues or changes in the appearance or odour of tap water.
Follow-up actions: Start on the day you receive notification
After you take immediate steps to protect the health of the people connected to your supply, you must continue to investigate the incident, monitor the supply and respond appropriately to new findings.
Keep the Authority informed as you investigate, as things change and as new information comes to light.
Click the headings below for actions to take on the day of detection after initial public health protections are in place.
Test additional samples
Follow-up samples should be taken from multiple locations across your supply. Include the original location of concern, and nearby upstream and downstream locations including reservoirs. Where possible, samples should be taken on the same day as the initial result was received. If this isn’t possible, they should be taken first thing the next morning.
If follow-up sampling detects further microbiological indicators, such as E. coli or total coliforms, issue a Boil Water notice immediately.
Keep the Boil Water notice in place until the incident is resolved
The Boil Water notice must be kept in place until:
- you have identified the most likely cause of contamination
- you have taken action to prevent further contamination
- any immediate and serious risk to consumers has been eliminated
- you have demonstrated and documented to the Authority’s satisfaction that public health is protected without a Boil Water Notice, or
- consecutive follow-up sample results and other findings demonstrate that ongoing contamination of drinking water is unlikely and the incident has been resolved.
Investigate contamination issues in depth
Keep investigating and reviewing information until you find the source or most likely cause of the problem.
Click on the headings below for key lines of inquiry to investigate.
Source water quality
A contamination event in source water, or a natural event, can change source water quality and challenge the treatment plant.
Review source water quality history for sudden changes in parameters, e.g. turbidity, temperature, flow, pH, ultraviolet transmittance, electrical conductivity.
Inspect the source intake and surrounding area for damage or interference from weather events, wildlife/stock animals, wastewater overflows, and any changes in areas surrounding and/or upstream of abstraction.
Treatment plant performance
Treatment plant barrier may have failed and allowed contamination to pass through to distribution.
Confirm treatment barrier performance has been retained by reviewing plant data. Check for stability and compliance, operating limits (e.g. critical control points for chlorine, ultraviolet intensity, turbidity, pressure differentials, etc), valve adjustments/bypasses, power outages or ‘brown outs’, maintenance activities and any other failures or issues.
Distribution water quality
General indicators of water quality can be used for investigative purposes and risk assessment.
Check other water quality parameters from the same sampling point, follow-up samples, other samples from across the network, and network data for trends and changes from expected ranges, e.g. lower free available chlorine, increased turbidity, pH changes.
Review log of recent events, supply trends across the network and any recent water quality changes.
Distribution integrity
Loss of integrity of distribution network can introduce contamination.
Ensure integrity and security of distribution systems in affected area have been retained, e.g. positive pressure maintained and no pressure transients, reservoirs are secure and free from contamination.
Check for recent backflow and cross-connection inspections, leak detection surveys, work orders and contractor reports of any recent, planned or reactive maintenance activities. Find out if public complaints or concerns have been raised and if there is any connection to areas with known issues, such as persistently low pressure.
Sampling tap and procedure
Poor condition of sampling point and poor aseptic procedure can compromise sample collection.
Review the condition and suitability of the sample point. Consider possible environmental factors of nearby land use and exposure of tap to environment. If any other samples were taken and transported together that day, check if they were delivered to the lab in a suitable condition.
Review sampling procedures and records, including sampler competency. Verify proof of competency assessment records and refresher training where applicable.
Laboratory process and procedures
Poor laboratory process and procedures can compromise sample testing.
Review lab quality control report and notes about any issues or concerns. Request re-analysis where possible and discuss result with laboratory.
The response is not complete until the most probable cause is addressed and you have reported on your investigation.
Click on the headings below for conclusion and reporting expectations.
Identify the cause (or most probable cause) of contamination
Initial investigations may identify one or more potential causes. Conduct further investigation to determine the root causes and contributing factors so that effective remedial and preventative actions can be implemented.
Take actions to address the most probable cause
Find and fix the most probable cause of the contamination and any other contamination risks identified during your investigation. Actively searching for and fixing issues in operations or infrastructure across the supply contributes to the protection of public health and enables continuous improvement.
We expect you to review the effectiveness of the actions you have taken. Any significant changes should be recorded in an update to the supply’s Drinking Water Safety Plan.
Submit an initial investigation report to the Authority within a week
An interim report detailing initial findings and planned actions is expected within a week of detection. If a Boil Water notice was not issued, or if it has been lifted, your report should collate the evidence you have already provided to the Authority and include any further analysis or discussion relevant to that decision.
This report is not expected to be comprehensive. An email update is sufficient.
Submit a full incident/investigation report to the Authority within eight weeks
A full report on the incident is expected to be submitted to the Authority within 8 weeks of the initial detection. Include details of improvements and remedial actions taken in response to the failure, an analysis of their effectiveness, and commentary on compliance with response procedures and timeframes.
We expect the full report to include an analysis of possible causes, identification of the cause (or most probable cause), and any corrective or preventative measures you have taken to stop future E. coli detections.
The report should note timeframes of actions taken and identify whether the expectations outlined above were met.
The Authority treats E. coli detection very seriously and will take action if water service providers fail to implement effective measures to ensure problems do not recur.
This webpage is a guideline only and does not address every situation that may occur in a drinking water supply. It is not intended to be definitive and is not legal advice. Drinking water suppliers are responsible for understanding and complying with their legislative duties. The Authority may review and revise this guidance over time. If you are using a printed copy, please check the website to make sure it is up to date.