NSW Health Response Protocol: following failure in water treatment or detection of giardia or cryptosporidium in drinking water
NSW Chief Health Officer Responsibility
The NSW Chief Health Officer has the responsibility for issuing advice to the public regarding measures available to minimise risk from disease, including water-borne disease.
In relation to drinking water, this responsibility requires the Chief Health Officer to rapidly assess any report of:
- breakdown in the water treatment system;
- contamination of the water supply; or
- clusters of illness potentially due to the former
and ensure action is promptly taken to address the problem including issuing a boil water alert (where appropriate).
1. Breakdown in the water treatment system
A failure of water treatment or disinfection will trigger an investigation by the water utility.
In the case of disinfection failure, the Chief Health Officer will consider the need for a boil water alert where an adequate disinfection residual cannot be maintained at the last point of primary disinfection before the consumer.
The Chief Health Officer will consider the need for a boil water alert in the case of treatment failure where treated water turbidity is not satisfactory and water cannot be diverted before entering the water supply system, and either:
1. there is rapidly changing raw water turbidity which cannot be improved by changing the level of offtake or source, or
2. there has been an influx of water from a contaminated source in the catchment in the last week (even if raw water turbidity is not rapidly changing).
3. The disinfectant and turbidity thresholds for the Sydney water supply have been determined and are summarised in the attached flow chart.
2. Investigation of Positive Findings 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 the water utility for potential failures of water treatment (see below). There is separate response protocol following the detection of E. coli. The water utility will inform NSW Health of positive Giardia or Cryptosporidium results within one hour. In the case of Sydney Water Corporation, notification will also be made to Sydney Catchment Authority within one hour.
2.1 The investigation triggered by a positive finding should include (but not be limited to) an assessment of:
a) the accuracy of the findings (i.e., confirmation that parasites are present);
b) chlorination;
c) flocculation and filtration;
d) presence of E. coli, total coliforms and total heterotrophic bacterial counts;
e) pre-treatment contamination of the raw water;
f) post-treatment contamination of the water (e.g., local ingress of material) and
g) turbidity in raw and treated water and particle counts where available.
If Cryptosporidium is detected, immediate re-sampling of the affected part of the system, adjacent areas of the system and areas downstream from the affected area of treated water, will be carried out. If Giardia is detected (but not Cryptosporidium), NSW Health and the water utility will review the conditions of disinfection in order to determine the need for resampling.
2.2 The water utility will move to correct any deficiencies and keep NSW Health advised where:
a) chlorine levels are found to be inadequate, or
b) E. coli is detected in treated water or total bacterial counts are elevated, or
c) flocculation or filtration systems are found to be failing, or
d) a recent contamination of the raw water is identified, or
e) a contamination of treated water is detected.
The Chief Health Officer will consider the need for a boil water alert, and other public health response or the convening of the Expert Panel, where:
a) any of the criteria listed in 2.2 above exists; and
b) there is detection of Cryptosporidium or Giardia.
3. Role of the NSW Health Expert Panel
The Expert Panel which has assisted the Chief Health Officer to date will have a permanent ongoing role as a Standing Committee. The advice of the Expert Panel will be valuable to assist the Chief Health Officer in making a decision on the most appropriate health response.
The Chief Health Officer will seek advice from the Expert Panel in situations including the following:
a) where deficiencies specified in 2.2 above are identified and it is still possible that persons will consume inadequately treated water (as advised by the water utility) but the health consequences are unclear and/or
b) where the results of re-sampling (as specified in 2.1 above) indicate that the contamination is persistent, but no deficiencies are identified and/or
c) 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, s/he may seek advice from the Expert Panel.
4. Public Health Action
In deciding on the issuing of a boil water alert, the Chief Health Officer will consider:
- detected levels of contamination;
- viability of organisms versus effectiveness of disinfection;
- time and scale of exposure including the likely recency of the 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 Expert Panel.
Protection of public health is a dominant element. The Chief Health Officer must also consider the possible adverse consequences of a boil water alert for example - scalds.
The potential responses available to the Chief Health Officer include:
- no further public health response required and continued surveillance for illness;
- issuing of public reminders of precautionary measures for immunocompromised individuals and possibly other groups with higher risk of secondary infection (nursing homes, preschools, daycare centres).
- boil water alert;
- public alert for need for increased hygiene measures.
The option chosen would clearly depend on the assessed level of public health risk and the potential benefits to the community or specific groups within the community from that response. For example, where results of a routine test are positive but subsequent tests are clear, and continued exposure to contaminants is unlikely, then there is no clear public health benefit from calling a boil water alert. However, it maybe useful to increase surveillance for illness and to continue to monitor the situation closely.
5. Lifting the Boil Water Alert
The NSW Chief Health Officer has the responsibility for lifting boil water alerts. The Chief Health Officer will take into account the following factors:
- detected levels of contamination;
- viability 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, which may be associated with delaying lifting.
This web page is managed and authorised by Environmental Health of Centre for Health Protection of the NSW Department of Health. Last updated: 31 March, 2009