10.2.2 Short-term evaluation of drinking water quality monitoring
Water utilities should always aim to supply drinking water that complies with the health-based and aesthetic guideline values and the microbial health-based targets detailed in these Guidelines.
If the results of drinking water quality monitoring within the distribution system show that the water being supplied to consumers does not comply with the relevant health-based and/or aesthetic guideline values and/or the microbial health-based targets, then corrective action should be taken, as detailed in the following sections.
Evaluating short-term microbial quality
The short-term performance measure for microbial quality is detailed in Table 10.1.
Table 10.1 Performance measure for Escherichia coli within the distribution system
Escherichia coli (E. coli) should not be detected in a minimum 100mL sample of drinking water
If detected, immediate corrective action must be taken
Water suppliers should take all reasonable actions to meet the guideline for E. coli, which is that E. coli should not be detected in a minimum 100 mL sample of drinking water. In practice, E. coli may occasionally be present in drinking water in the absence of any identifiable source of faecal contamination. Nevertheless, if samples taken are found to contain E. coli, the response to each detection should be rigorous:
Action should be taken urgently to identify and rectify any barrier breaches, and ensure that all the barriers are working continually and the system is safe. This should include checking disinfectant residuals.
Further samples should be collected to confirm the presence of E. coli and determine possible sources and distribution. This should include a repeat sample from the point where the non-conforming sample was collected and, as appropriate, an upstream sample (e.g. a service reservoir or system entry point) and a downstream or adjacent sample (e.g. a nearby sampling location).
An investigation should be initiated immediately to identify the underlying cause(s) of any barrier breaches or unexplained results, and put in place corrective actions to prevent future faecal contamination and detection of E. coli.
Further sampling should be undertaken to verify that the corrective actions have been effective.
All actions taken in relation to the detection should be documented.
If any of the repeat samples returns a positive result for E. coli, the response needs to be escalated. Depending on the circumstances, the escalation may involve:
additional water treatment, including increased disinfection and spot dosing with chlorine;
provision of an alternative water supply;
issuing of a boil-water advisory (based on advice from, or done in consultation with, the relevant health authority or drinking regulator).
Additional, more widespread monitoring of the supply system should also be undertaken to determine the extent of contamination.
Procedures on reporting and responding to E. coli detections should be established with the relevant health authority or drinking water regulator, and should be included in incident protocols. The procedures should include agreement on the requirements to be met before an incident is deemed to be closed.
Detection of E. coli in the drinking water system is a serious issue. At the conclusion of any incident, a debrief should be held to assess the problem and response, and agree to any short- and long-term actions needed to prevent a recurrence. Responsibility for undertaking those actions should be clearly established. If no identifiable source of contamination is determined, a long-term review of microbial system performance should be triggered to look for any emerging problems or trends.
Box 10.3 provides an example of a response protocol for E. coli detections.
Example response protocol for E. coli detections
Notification of the relevant health authority or drinking water regulator and immediate implementation of measures to render the water supply safe, as a priority. For chlorinated systems, establishing a free chlorine residual throughout the distribution system provides a high level of assurance that bacterial contamination will be inactivated. Actions that can be taken to increase residuals in the water supply system include increasing disinfection (e.g. chlorine dose rate), tank disinfectant dosing, mains flushing, and localised disinfection.
Disinfection residuals should be frequently monitored to provide assurance that this barrier to contamination is being continually maintained in the distribution system during the incident. This may be achieved by grab sampling or, preferably, installation of mobile monitoring.
A repeat sample for E. coli should be taken from the same sample point within 24 hours of the initial E. coli detection, to assess the effectiveness of remedial actions.
Rapid investigation from catchment to tap to identify the contamination source or reason for the barrier breach. This includes gathering relevant information on water treatment performance and other operational data, including any consumer complaints, and initiating surveillance in the catchment/reservoirs, treatment plant and distribution system to assess any non-routine or unusual activities that may have occurred or are occurring.
E. coli samples should also be concurrently taken from all other sample points within the supply zone, e.g. at the reservoir/tank outlet, downstream and adjacent points in the distribution. The purpose is either to confirm that the supply zone is free of contamination or to indicate the extent of any contamination.
Outcomes of the repeat samples should be immediately reported to the relevant health authority or drinking water regulator. If any repeat samples are positive, then further actions to protect public health will be determined.
Two more sets of repeat samples from all sample points in the zone should be taken over the following week to provide assurance that the system has returned to operating within specification.
Conduct a rapid investigation from catchment to tap to identify the contamination source or reason for the barrier breach. This includes gathering relevant information on water treatment performance and other operational data including any consumer complaints, and initiating surveillance in the catchment/reservoirs, treatment plant, and distribution system to assess for any past or present activities that are non-routine or unusual.
Investigation should also include possibility of sample errors or sample contamination as a result of sampling conditions or transport, as well as laboratory quality assurance and possible analytical issues.
Short-term corrective actions to eliminate any identified source of contamination or reasons for the positive result.
Close liaison should be maintained with the relevant health authority or drinking water regulator throughout the incident. The relevant health authority or drinking water regulator will determine the need to initiate emergency response plans, including issuing a public advisory, depending on the individual circumstances, the location of the sample and the investigation outcomes, and whether the sample represents a significant health threat to consumers.
Naegleria fowleri
An emerging issue in many jurisdictions is the detection of the free-living pathogenic amoeba Naegleria fowleri.
As free-living environmental organisms, Naegleria are not associated with faecal contamination and can be detected in the absence of E. coli. N. fowleri causes the waterborne disease primary amoebic meningoencephalitis (PAM). The route of infection is intra-nasal and PAM is associated with bathing rather than ingesting water.
Only N. fowleri has caused PAM. Other species of thermophilic Naegleria, however, may indicate the potential presence of N. fowleri, and detection of any Naegleria in drinking water should therefore be taken seriously, and corrective actions should be initiated while speciation is undertaken to determine if N. fowleri is present.
Naegleria are most likely to enter a water supply system at the source or at breaks in the sealed system such as open reservoirs and tanks. Under favourable conditions, they can proliferate in pipework and tanks. Naegleria can encyst and when in this state are more resistant to disinfection. Unless chlorine residual is continuous, the cysts are also able to survive in tank sediments and pipe biofilm.
Free chlorine or chloramine residual at 0.5 mg/L or higher will control N. fowleri provided the disinfectant residual persists throughout the water supply system at all times. A detection of thermophilic Naegleria in the treated water system should be taken seriously, as it indicates the potential presence of the pathogen N. fowleri, and that preventive measures and barriers have failed.
Box 10.4 provides an example of a response protocol to the detection of Naegleria.
Example response protocol for Naegleria fowleri
A detection of thermophilic Naegleria in the treated water system should be taken seriously as it indicates the potential presence of the pathogen N. fowleri, and that preventive measures and barriers have failed.
Immediate response should include the following:
Notify the relevant health authority or drinking water regulator and as a priority, take immediate action to render the water supply safe. To re-establish control of the water supply system, utilities should aim for free chlorine and chloramine residuals of at least 1 mg/L throughout the distribution system. Actions to increase residual in the water supply system include increasing disinfection (e.g. chlorine dose rate), tank disinfectant dosing, mains flushing, and localised dosing.
Check disinfection residuals frequently to provide assurance that this barrier to contamination is being continuously maintained in the distribution system during the incident. This may be achieved by grab sampling or, where available, by installing mobile chlorine monitors.
Arrange speciation of the Naegleria if not provided with the original laboratory notification.
Take a repeat sample for Naegleria from the sample point to assess the effectiveness of remedial actions. Naegleria samples should also be taken concurrently from all other sample points within the supply zone (e.g. at the reservoir/tank outlet, downstream, and adjacent points in the distribution). The purpose is either to confirm that the supply zone is free of Naegleria, or to indicate the extent of the problem.
Investigate from catchment to tap to identify possible barrier breaches or contributing causes. This includes gathering relevant information on water treatment performance and other operational data such as consumer complaints of dirty water, burst mains, tank running empty, or flow reversals in water mains. Any disturbance of sediments increases the likelihood of Naegleria detection.
Communicate the results of the speciation immediately to the relevant health authority or drinking water regulator. If N. fowleri is detected, consider further actions to protect public health, depending on the penetration and consistency of chlorine residuals in the distribution system.
Report outcomes of the repeat samples immediately to the relevant health authority or drinking water regulator. If any of the repeat samples are positive, then further actions to protect public health will be determined.
Take another set of repeat samples from all sample points in the zone over the following week to provide assurance that the system has returned to operating within specification.
Take short-term corrective actions to eliminate any identified source of Naegleria or reasons for the positive result.
Close liaison should be maintained with the health authority throughout the incident. The relevant health authority or drinking water regulator will determine the need to initiate emergency response plans, including issuing a public advisory.
At the conclusion of the incident, a debrief should be held to assess the problem and response and agree on any short and long-term actions needed to prevent a recurrence. Responsibility for undertaking those actions should be clearly established.
Actions that should be considered following a Naegleria detection include:
Review operational limits for chlorine/chloramine residuals in the distribution system to ensure a minimum of 0.5 mg/L is maintained at all times
Review the frequency of cleaning to minimise sediment build-up in tanks and reservoirs
Introduce flushing and scouring programs to control sediment build-up in water mains
Install temporary chlorine boosters to ensure continuous residual above 0.5 mg/L
Modify system operation to reduce water age and stagnation to promote maintenance of chlorine residuals
Take proactive measures to strengthen barriers when the challenge temporarily increases (e.g. increase chlorine residuals in the distribution system following a flow reversal event).
Evaluating short-term health-based chemical quality
The short-term performance measure for health-based chemical characteristics is detailed in Table 10.2.
Table 10.2 Performance measure for health-based chemical characteristics within the distribution system
Chemical characteristics should not be detected in drinking water at concentrations above the relevant health-based guideline value.
If a chemical characteristic is detected at a concentration above the relevant health-based guideline value, follow-up action must be taken.
Water suppliers should take all reasonable actions to ensure that drinking water does not contain any chemical characteristic in excess of a health-based guideline value, or an agreed level of service.
As described in Chapter 6, guideline values in the Australian Drinking Water Guidelines are generally rounded to a single significant figure. When interpreting monitoring results, water regulators and suppliers need to be aware that the guideline values are the results of rounding, and that the level of precision is one significant figure. When comparing a monitoring result with the guideline value the comparison should occur at the level of one significant figure. In determining compliance, state and territory water regulators can provide guidance.
Table 10.3 Examples of comparing monitoring data to guideline values
2 mg/L
1.6 mg/L
2 mg/L
Does not exceed guideline.
1 mg/L
1.4 mg/L
1 mg/L
Does not exceed guideline.
1 mg/L
1.5 mg/L
2 mg/L
Exceeds guideline.
500 mg/L
547 mg/L
500 mg/L
Does not exceed guideline.
0.05 mg/L
0.0523 mg/L
0.05 mg/L
Does not exceed guideline.
With a few exceptions (e.g. nitrate, copper, sulfate, fluoride), all health-based guideline values relate to lifetime exposure, such that a single result above the guideline value is unlikely to present an immediate health risk. Nonetheless, each result above a health-based guideline value or an agreed level of service should be investigated to ensure that it does not pose any short-term acute effects or represent an emerging issue. Such results may at least indicate that a problem has occurred somewhere in the system with respect to barrier performance, and this should be investigated.
Further information on how to manage instances where short-term exceedances occur is available in Section 9.12.
The recommended response to any detection of a chemical characteristic at concentrations above the relevant health-based guideline value is as follows:
The detection is to be reported to the relevant health authority or drinking water regulator, following established reporting protocols. Any health implications of the exceedance or non-conformity should be quickly assessed in relation to any short-term acute effects of the chemical in question, as this will influence the response.
The water supply system should be inspected, and treatment records should be reviewed to ensure that if treatment barriers have been applied to manage the particular chemical characteristic (e.g. arsenic removal), they have not been compromised.
Further sampling should be undertaken to verify the persistence and extent of the contamination. Sampling should also be undertaken to verify that corrective actions have been effective. The additional sampling should include a repeat sample from the point where the non-conforming sample was collected and, as appropriate, samples from source waters, upstream points (e.g. a service reservoir or system entry point) and a downstream or adjacent location (e.g. a nearby sampling point).
All actions taken in relation to the detection should be documented.
A public advisory would not normally be required unless the concentrations found are so high that an acute health impact is possible. However, if any of the follow-up samples return a result above the relevant health-based guideline value, the issue needs to be discussed with the relevant health authority or drinking water regulator. Depending on the circumstances, the discussions may result in:
additional, more widespread monitoring of the supply system to improve understanding of the problem;
operational changes to reduce the exposure;
provision of an alternative water supply;
longer-term improvements (e.g. additional treatment); and
issuing of public advice.
Evaluating short-term aesthetic quality
The short-term performance measure for chemical and physical characteristics with aesthetic guideline values is detailed in Table 10.4.
Table 10.4 Performance measure for aesthetic chemical and physical characteristics within the distribution system
Aesthetic chemical and physical characteristics should not be detected in drinking water at levels outside relevant aesthetic guideline values or agreed levels of service.
If an aesthetic chemical or physical characteristic is detected at a level outside relevant aesthetic guideline values or agreed levels of service, follow-up action should be taken.
Whilst not presenting a health risk, the aesthetic guideline values ensure that drinking water is aesthetically pleasing and pleasant to drink. Many customers equate aesthetics with the safety of drinking water, so every effort should be made to meet the aesthetic guideline values.
The recommended response to any detection of a characteristic outside the relevant aesthetic guideline value is as follows:
Inspect the water supply system and review treatment records to ensure that barriers have not been compromised.
Undertake further sampling to verify the persistence and extent of the issue. Sampling should be from the point where the non-conforming sample was collected plus, as appropriate, an upstream sample (e.g. a service reservoir or system entry point) and a downstream or adjacent sample (e.g. a nearby sampling location).
It should be noted that some aesthetic characteristics, such as pH and turbidity, have an association with the safety of drinking water supplied as they affect treatment effectiveness.
Some water supply systems may consistently not meet an aesthetic guideline value because of the nature of the source water (e.g. high total dissolved solids). In these specific cases, investigating the reason for each elevated result is not recommended; rather, a normal operating limit or range should be established based on historical data. Any monitoring results outside these limits would then be assessed as unusual and would indicate a change in system operation that requires further investigation.
In many of the supplies where the nature of the source water results in ongoing non-compliance with an aesthetic guideline for a chemical or physical characteristic, an agreed level of service may be established with regulators and consumers. The agreed levels of service then become the values against which performance is measured.
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