Health-based targets provide an assessment of the microbial safety of drinking water, including assessment of catchment risks and water treatment requirements. Water utilities in regional NSW should work towards incorporating health-based targets into their drinking water management systems. NSW Health and the Department of Planning and Environment - Water have developed guidance to support water utilities incorporate health-based targets into drinking water management systems and Section 60 approvals. 

Last updated: 01 August 2023

​Health-based targets for existing drinking water supplies

Water utilities need to continue to manage their drinking water supplies according to their drinking water management system. Water utilities should work toward having all drinking water supplies meeting the microbial health-based targets (HBT). Incorporating microbial HBTs into drinking water management will take time, particularly for small water suppliers.

Water utilities should assess all water supply systems against HBT guidance. NSW Health and DPE Water are available to support these assessments. The findings should be used to review and update the drinking water risk assessment and drinking water management system improvement plan. Water utilities should develop a plan to address those systems that do not meet HBTs. This plan should be documented as part of strategic planning, particularly when addressing the ‘Understanding water quality’ strategic planning outcome area under DPE Water’s strategic planning assurance framework. The highest priority for action by water utilities should be those supplies that have the greatest treatment deficit.

Across NSW, the highest priority systems have been identified as high risk by the NSW Health Cryptosporidium risk assessment or otherwise identified as level 5 risk for water quality via the Safe and Secure Water Program. Supply systems that are two or more log reduction values (LRV) short of the protozoan target have been rated as high risk by NSW Health. This is consistent with the Australian Drinking Water Guidelines (the Guidelines) recommendation that a two log deficit indicates the need for a new treatment barrier.

DPE Water can assist with guidance on optimising existing treatment processes to meet the recommendations of the Guidelines. This will provide greater confidence in drinking water quality while water utilities are implementing a plan to incorporate microbial HBTs into their drinking water management system. Improved control of pathogens may also be achieved by improved catchment management.

Generally, water utilities do not need to seek a third party assessment of HBT risks. The NSW Health Cryptosporidium risk model satisfies the requirements of the Guidelines and estimates the catchment risk for all three pathogen types. However, some groundwater sources may need a more detailed assessment. Water utilities should talk with their Public Health Unit before pursuing any assessments.

Log reduction values

A log reduction of a risk means that 90% of the existing risk has been removed. Below are some log reduction values to demonstrate the pattern

​Log reduction value
​Percentage risk removed​Percentage risk remaining

NSW Health will work with water utilities and their contractors to determine whether there are any deficits in a proposed treatment process specifically for bacteria and viruses. Such deficits relate to problems achieving adequate C.t (chlorine concentration and contact time) or UV dose using existing disinfection processes, or disinfecting unfiltered surface water. These deficits will become part of the drinking water design safety risk assessment submitted as part of DPE Water’s Section 60 approval process.

NSW Health and DPE Water position on addressing HBTs

  • Local water utilities should develop a plan in their drinking water management system Improvement Plan and other relevant strategic planning documents to address HBT shortfalls in all existing water supplies. Utilities should review NSW Health Cryptosporidium risk ratings and the Guidelines catchment categorisation, and identify any HBT shortfalls for pathogens. Utilities should engage with NSW Health and DPE Water to determine the priority for managing the LRV deficits in their supplies.
  • New water treatment plants should be designed to meet HBTs.
  • Existing water treatment plants should be upgraded to meet the microbial HBTs when a new source is introduced that has a higher catchment risk than the original source.
  • Existing water treatment plants may be incrementally upgraded to address a HBT deficit in an existing source, such as where there are not sufficient funds to meet the HBT.

Examples of new plants, new sources and upgrades of existing plants

New plant

A water utility is planning to install a new conventional filtration unit in a system that already has chlorine and UV disinfection. This is considered to be a new plant because of the significant change in treatment process and the scale of the work. The new plant must meet HBT guidance. This will be assessed during the Section 60 application.

New source

A water utility is installing a new intake pump for its water treatment plant in a location that receives stormwater from the town. This gives access to more water during storms, but the water is likely to contain more pathogens, particularly from sewer overflows. The plant receiving this new source of water needs to be upgraded to meet the microbial HBTs. Another utility is drilling a bore into an aquifer from which they already draw water. The water treatment plant receiving this bore water does not need to be upgraded to meet HBTs because the new bore has the same risk as the original water source (but needs a plan for upgrading if the existing system does not meet the HBT).

Plant upgrades

A water utility is planning to install a UV disinfection unit as a preliminary barrier to protozoa in an unfiltered system that already has chlorine disinfection. Another utility is installing a clarification process to convert its direct filtration plant to a conventional plant. A third utility is installing online turbidity monitoring on each of its filters. All of these are considered upgrades; they move a system closer to meeting the HBT and will be supported by DPE Water and NSW Health, even if they do not bring the plant fully to the target. The water utilities need to have a plan in place to meet the HBT.

Assessing treatment requirements to inform infrastructure design

The LRV targets for the catchment risk categories published in Table 5.5 of the Guidelines (see below) should be used in designing treatment plants and upgrades, and will be applied in Section 60 assessments. These values determine the amount of treatment needed to address the catchment risk and supply water that meets the HBT.

Australia Drinking Water Guidelines Table 5.5 - Treatment targets for protozoa, bacteria and viruses given the source water type and E. coli results

Source water category LRV target to achieve 1x10-6 DALYs per person per year

The LRV for treatment processes published in Table 5.6 of the Guidelines should be used in designing treatment plants and upgrades. These values will be applied in Section 60 assessments. Water utilities can seek to claim LRV other than those listed in the Guidelines. However, they will need to provide good evidence, such as manufacturer validation results or results published in the scientific literature. The same is true for claiming LRV for processes that have not been rated in the Guidelines for pathogen removal, such as biologically activated carbon. In-situ validation in drinking water would require dosing water with known numbers of pathogens to test the efficacy of removal (challenge testing). This process is time consuming, expensive, complex, and impractical, and so is not recommended.

NSW Health Cryptosporidium risk assessment

Utilities should engage with NSW Health at the start of, and throughout, a project to assess the catchment risk and determine the HBT treatment requirements. On request, NSW Health can provide the source water category based on the  Cryptosporidium risk assessment. This is useful for assessing the deficit from new water sources and informing treatment requirements for new plant designs.

Assessing pathogen risks from catchments

A water utility is planning to design and build a new water treatment plant for a surface source. They need to identify how great a pathogen risk they face from their catchment to determine what log reduction value (LRV) of treatment needs to be achieved in the new plant. Looking at their NSW Health Cryptosporidium risk assessment they see that they have a high risk. However, this is for their water supply with its existing treatment barriers. On request, NSW Health provides them with the source water category (Category 4), based on the Cryptosporidium risk assessment. Using Table 5.5, this identifies a deficit of five log for Cryptosporidium and six log for virus to be addressed be able to meet the health-based target. The utility can then use the LRVs for treatment processes published in Table 5.6 of the Guidelines to inform the treatment plant design and demonstrate how the selected process options meet the required pathogen removal deficit. Utilities should also ensure that treatment plant designs are informed by a comprehensive risk assessment identifying all sources of water quality hazards such as chemicals.

E. coli monitoring

Despite the use of E. coli data to confirm catchment assessments in the Guidelines, NSW Health does not expect E. coli monitoring in source water. The NSW Cryptosporidium risk model provides a reliable assessment of catchment risk for NSW drinking water supplies. This supersedes the Guidelines statement that catchments should be assumed to be Category 4 in the absence of E. coli data. Water utilities that want to assess source water quality by monitoring for E. coli should discuss their plans with their Public Health Unit. E. coli results should be interpreted in consultation with NSW Health and DPE Water.

Multiple barrier approach to pathogen management

The Guidelines recommend using multiple barriers against pathogen risks. The LRV requirements for higher risk catchments have been set to guide utilities into establishing multiple barriers.

For most practical scenarios, the Guidelines (Meeting the treatment requirements, page 94) suggests that the treatment implemented to reach the target may include:

  • Category 1 - Single barrier only of disinfection or filtration. This would most commonly be chlorination, but could sometimes be chloramination, UV or filtration.
  • Category 2 - Direct filtration (filtration without a sedimentation process between the coagulant dosing and filtration steps, or membrane filtration) followed by a single disinfection barrier. This disinfection barrier would usually be chlorine but sometimes chloramination or UV.
  • Category 3 - Full conventional filtration (filtration that has a sedimentation or a flotation process between the coagulant dosing and filtration steps) or membrane filtration following a sedimentation process, followed by a single disinfection barrier. The disinfection barrier would usually be chlorination but sometimes chloramination or UV.
  • Category 4 - Filtration followed by two disinfection barriers. The disinfection barriers would usually be UV and chlorine disinfection but sometimes chloramination or an additional filtration barrier may be applied. The second disinfection barrier, such as UV, is needed when a human pathogen risk is posed by sewage, including STPs and septic systems.

Other treatment options and combinations may be used, providing they are validated to deliver the required LRVs. Regardless of the disinfection process used to achieve the required LRV, residual chlorine disinfection should be maintained throughout the distribution system to provide protection from backflow and ingress and help to inhibit biofilm growth.

Using HBTs to inform the design of water treatment processes

Credit for media filtration

A range of LRVs for conventional filtration and direct filtration are quoted in Table 5.6 of the Guidelines. The upper values should only be applied to filters that can consistently operate below 0.2 NTU, with a critical limit of 0.5 NTU, continuously monitored with online individual filter turbidimeters, and with alarms linked into the plant SCADA. Additionally, the Guidelines note that “minimising turbidity spikes and controlling filter backwash and recycling procedures are consistent with achieving higher LRVs”. This is largely consistent with the assumptions of the NSW Health Cryptosporidium risk assessment model.

LRV credits for other barriers/treatment processes not included in the Guidelines

Membrane filtration with coagulation

LRV credits for virus removal will be considered for the combination of coagulation and flocculation with membrane filtration, in consultation with NSW Health and DPE Water.

Sedimentation and clarification

LRV credit for removal of all pathogens will be considered for clarifiers operating with coagulation but without a filter, including lagoon sedimentation clarifiers, in consultation with NSW Health and DPE Water. The principles of operation should be part of the utility’s drinking water management system.

Validation of treatment process performance

Utilities and contractors must follow manufacturer’s instructions on the installation and operation of a process to be able to rely on the validated performance of the process. The utility should ensure that a competent person provides a commissioning report that includes confirmation that the original validation criteria are satisfied (e.g. pipe specification, flow rate). Proof of commissioning to the manufacturer’s specification is essential.

Challenge testing for treatment validation does not need to be repeated where:

  1. a manufacturer has validated a treatment process, providing the operating conditions defined by the manufacturer are relevant to the site in question, or
  2. there are published LRVs or accepted industry norms.

For example, a manufacturer may specify that validation of a UV light disinfection system is only applicable for waters above a defined transmissivity (the percentage of UV light that passes through the water).

For chlorination, the required residual chlorine concentration (C) and the corresponding disinfectant contact time (t) in minutes (C.t) to achieve the specified LRV depends on temperature and pH. These conditions are specified in the Guidelines table 5.6.

In other cases, such as conventional and direct media filtration, LRVs can be adopted from accepted industry norms (e.g. USEPA 2006), providing defined operating conditions and operational monitoring targets are achieved. This includes both operational monitoring of target criteria, such as filter effluent turbidity, and applying good practice to operating supporting processes (e.g. coagulation, mixing, flocculation, sedimentation or flotation, filter ripening, backwash processes and controls on waste recycling). Operational monitoring and compliance with target criteria and critical limits, underpinned by good operational practices and supporting programs, is the key to ensuring that pathogen removal is maintained as expected.

Current as at: Tuesday 1 August 2023
Contact page owner: Environmental Health