NSW Health Sydney Water Response Protocol: Water treatment failure or detection of Giardia or Cryptosporidium in drinking water

Responsibilities

Sydney Water​

Sydney Water Co​rporation (Sydney Water) is required to report to NSW Health any event or information within its water supply system that may adversely affect public health.

NSW Chief Health Officer

The NSW Chief Health Officer has the responsibility under the Public Health Act 2010 to issue advice to the public regarding measures available to minimise risk from disease, including water-borne disease. The Chief Health Officer may from time to time decide, in relation to any supplier of drinking water:

• whether or not it should issue a boil water advice for the drinking water it supplies or has available for supply
• whether or not it should provide additional information to the public in connection with any boil water advice it issues, and/or
• whether or not a boil water advice is to be retracted or corrected.

This responsibility requires the Chief Health Officer to rapidly assess any report of problems related to drinking water and ensure action is promptly taken to address the problem. Problems related to drinking water may include:

• a breakdown in the water treatment system
• contamination of the water supply, and/or
• clusters of illness potentially due to the former.

Breakdown in the water treatment system

A failure of water treatment or primary disinfection will trigger an investigation by the Sydney Water.

In the case of treatment failure, the Chief Health Officer will consider the need for a boil water alert where treated water turbidity did not meet target and water can not be diverted before entering the water supply system, and:

• the inherent risk of Cryptosporidium in the catchment is medium or high, and/or
• primary disinfection target can not be met.

Examples of conditions that would be considered to increase catchment risk rating include (but are not limited to):

• the turbidity of the raw water is changing rapidly and can not be improved by changing the level of offtake or source, or
• there has been an influx of water from a contaminated source in the catchment in the last week (even if the turbidity of raw water is stable).

In the case of disinfection failure, the Chief Health Officer will consider the need for a boil water alert where an adequate disinfection residual can not be maintained at the last point of primary disinfection before the consumer.

The critical control point limits that indicate a failure of the treatment and disinfection systems for Sydney Water surface supplies have been determined in consultation with NSW Health and are summarised in the Response Protocol Flowchart.

Investigation of ​Cryptosporidium or Giardia detections in treated water

Where testing of treated water for Giardia cysts or Cryptosporidium oocysts has been performed, the detection of parasites at any level will trigger an investigation by Sydney Water for potential failures of water treatment. However, the detection of Cryptosporidium in water does not confirm whether the organism is viable or a risk of human infection. While there are more than 20 recognised species of Cryptosporidium, almost all identified cases of waterborne disease in humans have been caused by only two species. Sydney Water will inform NSW Health and WaterNSW of positive Giardia or Cryptosporidium results within one hour of receiving them. There is separate response protocol following the detection of E. coli.

The investigation triggered by a positive result should include (but not be limited to) an assessment of:

• the accuracy of the result (i.e., confirmation that parasites are present, presumptive viability)
• assessment of source water quality including any contamination in the catchment and raw water turbidity
• adequacy of treatment including flocculation, filtration and disinfection
• assessment of network performance including chlorine residual
• post-treatment contamination of the water (e.g., local ingress of material).

If Cryptosporidium is detected, immediate re-sampling should occur as it is resistant to chlorine disinfection. If Giardia is detected (but not Cryptosporidium), NSW Health and Sydney Water will review the conditions of disinfection in order to determine the need for resampling.

The Chief Health Officer will consider the need for a boil water alert or other public health responses (including the convening of the NSW Health Water Expert Panel) where Cryptosporidium or Giardia is detected and:

• a recent contamination of the raw water is identified, or
• treatment including flocculation, filtration and disinfection have not met targets, or contamination of treated water is detected (i.e., vermin found during inspection of network), or
• E. coli is detected in treated water.

Role of the NSW Health Water Expert Panel

The NSW Health Water Expert Panel has a permanent ongoing role as a Standing Committee. The Chief Health Officer may call on the advice of the NSW Health Water Expert Panel when making a decision on the most appropriate health response in situations including the following:

• where it is possible that persons will consume inadequately treated water (as advised by Sydney Water) but the health consequences are unclear
• where the results of re-sampling indicate that the contamination is persistent, but no deficiencies in treatment are identified, or
• as otherwise required.

If an outbreak of illness occurs in the population due to infection with Giardia or Cryptosporidium, NSW Health will investigate and manage the incident following its standard procedures. If the Chief Health Officer has reason to suspect that the cause of the outbreak may be related to the consumption of drinking water, they may seek advice from the NSW Health Water Expert Panel.

Public health action

When deciding whether to issue a boil water alert, the Chief Health Officer will consider:

• detected levels of contamination
• viability and type of organisms versus effectiveness of disinfection
• likely ongoing exposure based on the occurrence and duration of contamination
• evidence of increased illness in the present or previous events
• the likelihood of effective identification and rectification of any water system problem
• the need to communicate accurate and appropriate information to the community in a timely and effective way
• the community impact of any public health action, and
• the advice of the NSW Health Water Expert Panel, if consulted.

Protection of public health is a priority. The Chief Health Officer must also consider possible adverse consequences of a boil water alert, such as scalds. The Chief Health Officer may decide not to issue a boil water alert if there is no clear public health benefit. For example, where results of a routine test are positive but subsequent tests are clear, and continued exposure to contaminants is unlikely. However, it may be useful to increase surveillance for illness and to continue to monitor the situation closely.

Other responses may include:

• issuing a public reminder of precautionary measures for immune compromised individuals or other groups with higher risk of secondary infection such as nursing homes, preschools and daycare centres, or
• issuing a public alert of a need for increased hygiene measures, or
• no further public health response required and continued surveillance for illness.

Lifting a boil water alert

The NSW Chief Health Officer has the responsibility to lift boil water alerts. The Chief Health Officer will take into account the following factors:

• detected levels of contamination
• viability and type of organisms versus effectiveness of disinfection
• duration and scale of exposure of the population to contaminated water
• evidence of increased illness in the present or previous events
• the likelihood of effective rectification of any water system problem
• the predicted clearance or flow time of clear water through the water distribution system
• the need for additional testing
• the need to communicate to the public which areas have been released from the boil water alert in a timely and effective way, and
• the adverse impact to the community associated with delaying lifting.

The Response Protocol Flowchart​ summarises the critical control point limits for treatment and primary disinfection processes for the Sydney Water supply.​