In the context of water quality management, monitoring is a generic term given to the sampling and subsequent analysis and recording of water quality parameters.
Sampling is typically undertaken via grab sampling or via an online instrument (composite samples are not often used in drinking water monitoring). The time, place, location and parameters sampled all depend on the context of the monitoring, and what information is required about a drinking water system to confirm the efficacy of water treatment and preventative measures, and thus the safety of the water for the community to consume.
Why Monitor?
Human beings are only able to discern the quality of water based on aesthetic characteristics, such as the colour, odour and clarity of water. Though these indicators are often useful for detecting issues with water (ADWG suggests recording and investigating customer complaints), this is not enough to determine that safety of drinking water, as microbial and chemical hazards in water are quite often invisible without the assistance of analysing equipment/methods. Therefore we rely on technology and methods which can give us insight into the composition of the water we drink, however factors such as the frequency, method and location (i.e. the context) of monitoring undertaken can drastically change the interpretation of results. This brings us to the different types of monitoring.
Different Types of Monitoring
Research (“Where are we now”):Water quality parameters investigated to gain greater insight into a new or existing drinking water system. Includes activities such as baseline monitoring, which entails testing existing/potential water sources to identify water quality problems (e.g. naturally high levels of fluoride in a bore).
Operational (“Is it working now?”): Undertaken in the source/catchment/treatment process/distribution system, ensuring processes and activities are working properly to produce and or deliver safe water quality. Ideally parameters monitored should be measured continuously, and permit rapid response to any problems detected. The operational monitoring should correspond with an acceptable operational range (referred to as an operational envelope) for each parameter, linked to alarms if parameters are detected outside these limits. Where there is a deviation out of the operational envelope there should be an operational response.
Verification (“Did it work?”): Monitoring undertaken of the product water, usually in the distribution system or representative of supplied water, to check the quality of water supplied to the consumer, including monitoring customer comments and complaints. This is intended to be representative of the water quality the end user is receiving.
Validation (“Will it work?”): Used to confirm that a treatment unit/process is capable of operating to the required level of performance (e.g. 3 log removal of Cryptosporidium, arsenic, etc). Note in some cases, if existing evidence is adequate, validation may be done as a desktop activity. When actual performance data (i.e. empirical evidence) is required for validating a system, validation monitoring is undertaken. Validation is also used to identify the operational envelope.
Why are there different types?
As discussed above, depending on the desired output (i.e. what information is required about a water supply system), the monitoring undertaken will differ. Sampling is quite often costly to water service providers, therefore it is important when designing a monitoring program to consider the outcome of the monitoring, as well as the context.
Limitations of monitoring
There is no doubt that monitoring plays an extremely important role in the delivery of water that is safe and fit for the intended purpose. It is integral to the implementation of water quality risk management frameworks, which are considered best practice.
However, there are some key limitations which must be considered. These includes:
Spatial and temporal variability in water produced and sampled. For example if a sample detects 0 cfu/100mL E. coli, it does not definitively mean there are no E. coli present. This is because it is often incorrect to assume a uniform dispersal of contaminations in a stream of water. This is also true of timing – if a single sample is taken on a weekly basis, although every sample may pass, there is no guarantee that there was no event in-between sampling.
Statistical significance of water sampling is difficult to achieve, due to associated costs and labour required to gather the number of samples required.
Continuous online monitoring equipment is only readily available for certain chemical and physical parameters. Microbial parameters must be collected as grab samples.
It is often too costly and difficult to monitor harmful pathogens directly, therefore other parameters are used to infer pathogen removal, for example turbidity is used as an indicator of filter performance and therefore can be used to confirm that the filter is effectively removing protozoa risk.
Calibration of online and benchtop equipment is very important to ensure data is accurate of the system – calibration requirements can often be overlooked.
Looking Forward
A preventive approach is a part of a risk based management framework, which is linked to Hazard Analysis and Critical Control Point (HACCP) and will soon be augmented by the introduction of Health-based Treatment Targets (HBTs). These frameworks are part of the water industry’s shift away from a reactive attitude to managing risks associated with water quality.
Traditionally verification (end user) samples have been heavily relied on to give indicators of overall system performance. However, due to the limitations discussed above this is no longer considered best practice. Under the preventive approach multiple barriers are in place to ensure out of specification water is not supplied to the end user. Operational monitoring provides real-time indication of barrier performance, allowing for timely corrective actions to be taken. Any monitoring programs designed should be risk based, with priority given to the highest risk and critical treatment processes.
For more information
The Australian Drinking Water Guidelines (2011) and Australian Recycled Water Guidelines (2008) detail the risk based approach to water quality management.
References
NHMRC, NRMMC (2011) Australian Drinking Water Guidelines Paper 6 National Water Quality Management Strategy. National Health and Medical Research Council, National Resource Management Ministerial Council, Commonwealth of Australia, Canberra
NHMRC, NRMMC & EPHC (2008) Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 2). National Health and Medical Research Council, National Resource Management Ministerial Council and Environment Protection and Heritage Council, Commonwealth of Australia, Canberra