Managing pathogen risks in drinking water: response protocol for water utilities and public health units

Water utilities must immediately notify the local Public Health Unit of any incident affecting the ability to provide safe drinking water.

This response protocol outlines the actions that should be taken by water utilities and public health units in responding to critical limit exceedances, raw water quality problems, reservoir contamination and test results indicating possible contamination.

The water utility is responsible to investigate and carry out corrective actions to restore control of treatment processes.

The PHU can support and advise the water utility on its investigation and response.

Prompt action will help prevent illness.

A boil water alert may be necessary when there is an ongoing risk.

This page forms part of the NSW Health response protocol for water utilities and public health units: Managing pathogen risks in drinking water​​​​ ​​

Introduction

This protocol was approved by the Chief Health Officer (version 3 March 2018).

This protocol provides processes that water utilities should follow in working with Local Health District Public Health Units (PHUs) in responding to risks to drinking water safety including where:

1. a critical limit has been exceeded at a critical control point (CCP) for pathogen risk
2. there is a raw water quality problem likely to affect water treatment
3. there is evidence of vermin (birds, possums or other animals) found in a reservoir
4. Escherichia coli (E. coli) is detected in drinking water

Responsibilities

The water utility is responsible for all necessary investigation and sampling as specified in this response protocol. The water utility should plan, carry out and document the investigation, response and corrective actions and communicate these to the PHU. Water utilities must immediately notify and consult the local PHU of any incident affecting the ability to provide safe drinking water. Prompt action at these times will help prevent illness.

The PHU can support and advise the water utility on its investigation and response.

The PHU will advise the Department of Industry – Water (DoI Water) Regional Officer when a drinking water risk is notified or when a boil water alert is considered or lifted. DoI Water can provide technical assistance to water utilities when responding to drinking water incidents.

Incident scenarios

A boil water alert should be considered where there is a risk that cannot immediately be rectified and consumers will be exposed to contaminated water.

A critical limit has been exceeded and/or there is a raw water quality problem likely to affect water treatment

Notification

The water utility must immediately notify and consult the PHU when:

• a critical limit at a CCP for pathogen risk is exceeded (e.g. filtered water turbidity is above the critical limit or chlorination contact time (C.t) below critical limit) (see NSW Health critical control point guidance), or where there is
• raw water quality problems (e.g. high or rapidly changing turbidity) mean that treatment processes may not be effective.

The water utility must still notify critical limit exceptions, even when the treatment or disinfection failure is corrected before inadequately treated water enters the supply system.

Response and investigation

The water utility should follow its CCP standard operating procedures (SOPs). SOPs (including CCP limits) should be displayed in the treatment plant. SOPs provide guidance on responding to critical limits, adjustment limits and target criteria exceptions and dealing with changes in raw water quality. Water utilities must respond promptly to adverse signals (including operational monitoring results, alarms, weather warnings).

The water utility should estimate how long demand will be met by the remaining safe drinking water in the distribution system. This will determine the time available to rectify the situation and/or consider a boil water alert.

The response may include:

• changing to an alternative source or changing the off-take depth to improve raw water quality
• assessing whether there have been recent inflows of water from contaminated sources in the catchment, (even if raw water turbidity is stable). Sources could include sewer overflows, sewage treatment plant discharges or storm runoff from intensive agriculture (See Sanitary survey guidance, section 4)
• investigating whether a temporary shutdown of the treatment plant is feasible if adequate storage is available
• optimising all processes at the treatment plant
• diverting filtered water to waste (when above target turbidity)
• investigate whether contaminated water can be isolated or removed from the system, e.g., by emptying or taking the reservoir offline. (Note that this will not be effective for consumers who receive water before the reservoirs.)
• confirming whether adequate disinfection residual is being maintained throughout the distribution system (free chlorine residual of at least 0.2 mg/L or total chlorine of at least 0.6 mg/L in chloraminated systems). Where there is a risk of Naegleria fowleri (see NSW Health Naegleria fact sheet), free chlorine residuals must be at least 0.5 mg/L
• where possible, monitoring turbidity in the distribution system
• boosting chlorine, if inadequate, at points in the distribution system (e.g., by dosing at mains and/or reservoirs)

Next step

Contact the PHU regarding the outcome of the response and investigation and the need for a boil water alert (See Boil water alert guidance, section 5).

There is evidence of vermin (birds, possums or other animals) found in a reservoir

Notification

The water utility must immediately notify and consult with the PHU when evidence of vermin is found.

Response and investigation

The response may include:

• assessing whether potentially contaminated water could be isolated or removed from the system (e.g. by emptying or taking the reservoir offline)
• confirming whether adequate disinfection residual is being maintained throughout the distribution system (free chlorine residual of at least 0.2 mg/L or total chlorine of at least 0.6 mg/L in chloraminated systems). Where there is a risk of Naegleria fowleri (see NSW Health Naegleria fact sheet), free chlorine residuals must be at least 0.5 mg/L.
• collect microbiology samples (for E. coli)
• boosting chlorine, if inadequate, at points in the distribution system (e.g. by dosing at mains and/or reservoirs)
• remove vermin and repair the reservoir to prevent recontamination.

Next step

Contact the PHU regarding the outcome of the response and investigation and the need for a boil water alert (See Boil water alert guidance, section 5).

E. coli is detected in drinking water

Notification

The testing laboratory must immediately call the water utility and the PHU when E. coli is detected in drinking water (E. coli indicates recent faecal contamination) and email or fax the result to the water utility and PHU.

The water utility should ask the laboratory for the chlorine concentration and any other field results (e.g. pH, turbidity) for the sample, if the utility does not have a record.

Response and investigation

The water utility and PHU should discuss the response to the detection.

The PHU will consider the need for a boil water alert if the water utility cannot provide prompt confirmation of normal operation, including an adequate disinfectant concentration at the sample site and throughout the system (See Boil water alert guidance, section 5).

The response may include:

• checking, correcting and/or adjusting treatment plant CCP performance particularly filtration (i.e. filtered water turbidity) and disinfection (i.e. chlorination C.t). (Note: Depending on the scale and source of contamination, an increase in disinfection at the treatment plant or reservoir may be sufficient to rectify the situation. If repeat testing again indicates contamination, further control measures including a boil water alert may be required.)
• confirming whether adequate disinfection residual is being maintained throughout the distribution system (free chlorine residual of at least 0.2 mg/L or total chlorine of at least 0.6 mg/L in chloraminated systems). Where there is a risk of Naegleria fowleri (see NSW Health Naegleria fact sheet), free chlorine residuals must be at least 0.5 mg/L
• boosting chlorine, if inadequate, at points in the distribution system (e.g., by dosing at mains and/or reservoirs)
• confirming the integrity of the distribution system, especially reservoir integrity. Identify any recent main break repairs and investigate whether they could be the source of contamination. (Note: before flushing mains, consider the risk that flushing may distribute contamination throughout the system if the source of contamination is unknown.)
• collecting repeat microbiology samples for E. coli (see below)
• investigating catchment conditions and raw water quality. (See Sanitary survey guidance, section 4)
• correcting any faults that are found.

Repeat microbiology testing

The water utility should:

• immediately re-sample at the same site and at least two other locations in the distribution system using NSW Health Drinking Water Monitoring Program ‘Repeat’ labels and record field results (free and total chlorine, pH, temperature and turbidity)
• collect samples from upstream and downstream of the original sample site to investigate whether the problem is localised or system-wide (and that there is adequate chlorine residual throughout the distribution system)
• submit the samples to a NSW Health laboratory or other NATA accredited laboratory for analysis. Advise the laboratory that these are urgent repeat samples to investigate possible contamination. Request that the laboratory urgently notify both positive and negative results.
• note that the PHU can request that the NSW Health laboratory conduct the analysis out of hours using the Urgent Water Analysis Request form.

Where immediate resampling is not possible (e.g. sampling officer is not available or it is not possible to meet departure time of a flight or courier), the water utility and PHU should assess the situation and agree on the necessary actions, and take a repeat sample as soon as practicable.

If E. coli is detected in the repeat samples, the response should include:

• checking, correcting and/or adjusting treatment plant CCP performance particularly filtration (i.e. filtered water turbidity) and disinfection (i.e. chlorination C.t). (Note: Depending on the scale and source of contamination, an increase in disinfection at the treatment plant or reservoir may be sufficient to rectify the situation. If repeat testing again indicates contamination, further control measures including a boil water alert may be required.)
• immediately contact PHU regarding the need for a boil water alert (See Boil water alert guidance, section 5).
• confirming whether adequate disinfection residual is being maintained throughout the distribution system (free chlorine residual of at least 0.2 mg/L or total chlorine of at least 0.6 mg/L in chloraminated systems). Where there is a risk of Naegleria fowleri (see NSW Health Naegleria fact sheet), free chlorine residuals must be at least 0.5 mg/L
• boosting chlorine, if inadequate, at points in the distribution system (e.g., by dosing at mains and/or reservoirs)
• confirming integrity of the distribution system, especially reservoir integrity
• conducting a sanitary survey (See Sanitary survey guidance, section 4).

If E. coli is not detected in the repeat samples and the supply system is operating normally resume normal water quality monitoring. The next scheduled sample would normally be sufficient as follow-up testing.

Total coliforms are detected in drinking water

Notification

The testing laboratory will email or fax the water utility and the PHU when total coliforms are detected in drinking water. Standard NSW Health laboratory microbiology testing includes both total coliform bacteria and E. coli.

Response and investigation

Coliforms, when used in operational monitoring, may indicate inadequate treatment, breakdowns in system integrity, or the presence of biofilms. (see Appendix 1 Indicator bacteria).

Note that where water utilities use total coliforms as an indicator of system cleanliness, organism numbers should be established on a system-specific basis, taking into consideration relevant historical data and an understanding of the characteristics of the system (such as maintenance of chlorine residual, long sections of mains).

The response may include:

• checking, correcting and/or adjusting treatment plant CCP performance particularly filtration (i.e. filtered water turbidity) and disinfection (i.e. chlorination C.t)
• confirming whether adequate disinfection residual is being maintained throughout the distribution system (free chlorine residual of at least 0.2 mg/L or total chlorine of at least 0.6 mg/L in chloraminated systems). Where there is a risk of Naegleria fowleri (see NSW Health Naegleria fact sheet), free chlorine residuals must be at least 0.5 mg/L
• confirming the integrity of the distribution system, especially reservoir integrity.

Next step

Refer to section 3.1 if a critical limit exceedance is identified.

Repeat testing

The next scheduled sample would normally be sufficient as follow-up testing.

Further information

Contact your local Public Health Unit on 1300 066 055 and refer to:

• the full NSW Health response protocol for water utilities and public health units: Managing pathogen risks in drinking water
• Response protocol flowchart
• Sanitary survey guidance
• Boil water alert guidance
• Appendix on indicator bacteria
• NSW Health Naegleria fact sheet.