A1.6 Preventive measures and multiple barriers
The identification, evaluation and planning of preventive measures should always be based on system-specific hazard identification and risk assessment. The level of protection used to control a hazard should be proportional to the associated risk.
The multiple barrier principle should be employed and preventive measures should be comprehensive from catchment to consumer. Wherever possible, the focus of these measures should be to prevent contamination in the catchment rather than to rely on downstream control. Box A1.1 (below) provides further information on catchment management and source water protection.
Summary of actions
Identify existing preventive measures from catchment to consumer for each significant hazard and event.
Determine the residual risk and assess that microbial, chemical and radiological health-based targets are met.
Evaluate alternative and additional preventive measures where improvement is required.
Document the preventive measures and strategies addressing each significant risk into a plan.
Establish mechanisms to ensure cooperation and development of action plans with external agencies.
Examples of preventive measures and management strategies from catchment to consumer are provided in Table A1.7. An indication of removals of enteric pathogens using the multiple barrier approach is provided in Table A1.8. Table A1.9, in the following section, also provides examples of preventive measures for Giardia from catchment to consumer for a river system.
Once preventive measures addressing each significant risk have been identified, the strategies should be documented into a plan. Any new preventive measures to be implemented over the longer term, such as covering water storages or the introduction of filtration, should be incorporated into an improvement plan (see Section 3.12.2 Drinking water quality management improvement plan).
Where responsibility for preventive measures lies outside the direct control of the drinking water supplier (i.e. with external agencies), mechanisms for communication to ensure cooperation and development of action plans should be established (see Section 3.1.3 Engaging stakeholders).
The combination of preventive measures applied for each drinking water systems should achieve compliance with identified microbial, chemical and radiological health-based targets (see Section 1.3).
Catchment management and source water protection
Catchment management and source water protection provide the first barrier for the protection of water quality. Catchment management usually involves a coordinated approach to develop short-term and long-term plans to enhance water quality and eliminate or control any potential sources of pollution.
Whether water is drawn from surface catchments or underground sources, it is important that the local catchment or aquifer is understood, and that the activities that could lead to water pollution are identified and managed. Effective catchment management and source water protection include development of a catchment management plan with the commitment of land use planning authorities to prevent inappropriate development and to enforce relevant planning regulations.
Catchment management plans
A comprehensive catchment management plan should be developed and implemented to mitigate any existing and potential future risks, and where practical, aim to improve the quality of water harvested over time. The plan should include, where appropriate, the following elements:
a policy statement identifying the protection of water quality as an explicit objective of local legislation
preparation and review of land use planning controls jointly with the planning authority
establishment of agreed processes and criteria for managing development applications
a clear statement of responsibilities of different agencies and agreed coordination processes
identification of water quality hazards, estimation of risks and planning of relevant management strategies
a monitoring program to identify pollution sources, maintain quality control, and collect long-term data to determine trends
regular documented inspections to monitor catchment conditions and land use changes
a community awareness program, including strategies for working with landowners to support the catchment management plan
agreed and tested emergency response plans with relevant emergency services for responding to major pollution events such as spillages or contamination.
The extent to which catchment pollution can be controlled or remediated is often limited in practical terms wherever there are competing water uses and pressure for increased development in the catchment. In devising catchment management plans, it may be necessary or useful to divide large catchments into smaller, more manageable units (e.g. subcatchments). Where this is done, it is important to ensure that, in combination, the various plans provide an integrated approach across the entire catchment. For large river systems protection may be possible only over limited reaches in the vicinity of the raw water off-take or reservoir inlet.
Planning controls
Well-designed planning regulations are a critical component of sound catchment management and protection of water quality. Where possible, protection of water resources should be included as a principal objective in planning policies.
Planning regulations should address management and control of high-risk development in catchments and aquifer intake areas (e.g. intensive animal feedlots) and should also address the issue of long-term incremental development. Urban development, agroindustry and general industry should be carefully scrutinised to ensure that they will not impact on water resources. On site waste treatment and disposal systems should be permitted only where sites are suitable and there is minimal risk to the water supply. Such systems should be designed, installed and maintained correctly, and inspected regularly. Defects should be reported and rectified.
Responsibility for the development and implementation of planning strategies and regulations is generally shared between state and local government agencies. It is important that drinking water suppliers and environment and health authorities establish strong links with planning agencies and take an active role in:
the development or amendment of these planning strategies and regulations
the evaluation of individual development proposals with respect to potential impacts on water quality or quantity.
Where appropriate, formal agreements should be required to ensure approval conditions are complied with and recorded on land titles to alert potential purchasers of the obligations associated with the property.
Community awareness
Community awareness programs should be developed to promote the protection of water quality. Support for local landcare and watercare groups is a relatively low-cost opportunity to develop community awareness and reduce pollution risks.
Diffuse sources of pollution arising from agricultural and animal husbandry activities are difficult to manage but their effect on water quality can be minimised by the use of best practice management such as fencing of streams, management of riparian zones and off-stream watering of stock. Landowners can be encouraged to protect stream banks and provide buffer strips through community awareness programs and by subsidising tree planting and fencing works.
Cooperation with landowners and close collaboration with agricultural agencies are essential for the management of point sources such as dairy effluent and stockyard runoff. Demonstration projects that aim to show the benefits of collecting and using this material are useful.
Table A1.7 Examples of preventive measures from catchment to consumer
Use of an appropriate source water
Ownership and control of catchment area
Designated and limited uses
Registration of chemicals used in catchments
Control of human activities within catchment boundaries
Control of wastewater effluents
Involvement in land use planning procedures
Participation of community and landowners within the catchment area
Regular inspections of catchment areas
Protection of waterways (fencing out livestock, buffer zones, management of riparian zones)
Runoff interception
Use of planning and environmental regulations to regulate potential water polluting developments
Use of industry codes of practice and best practice management
Control of water extraction
Alternate selection of water source
Use of available water storage for periods of heavy rainfall
Appropriate location and protection of intake
Proper well construction including casing, sealing and well-head security
Proper location of wells in aquifer
Water storage systems to maximise detention times
Infiltration wells
Enclosed water storages
Prevention of unauthorised access
Destratification of water storage
Diversion of stormwater downstream from intake
Roofed storages and reservoirs with appropriate stormwater collection and drainage
Securing tanks from access by animals
System maintenance
reservoir cleaning or scouring
pipeline flushing
fittings maintenance
Coagulation or flocculation and sedimentation
Alternative treatment
Use of approved water treatment chemicals and materials
Control of water treatment chemicals
Regular assessment of hazards and risks
Use of skilled and trained operators
Process controllability of equipment
Availability of backup systems
Water treatment process optimisation, including
chemical dosing
filter backwashing
flow rate
minor infrastructure modifications
Use of tank storage in periods of poor-quality raw water
Distribution system maintenance
Availability of backup systems (power supply)
Maintaining an adequate disinfectant residual
Cross-connection and backflow prevention devices implemented
Fully enclosed distribution system and storages
Secondary disinfection
Appropriate repair procedures, including subsequent disinfection of water mains
Maintaining adequate system pressure
Quality assurance and validation procedures for sampling and testing
Calibration and maintenance of equipment
Information dissemination:
responsibilities relating to drinking water quality
plumbing and appliances
backflow prevention
point of use devices
Table A1.8 Estimated removals of enteric pathogens using multiple barriers
Bacteria
0.5–1 log removal
No net removal due to recontamination from birds and small animals.
Conventional: 2 log removal
Direct: 1 log removal
Membraneᵈ: 4 log removal
Chlorine, chlorine dioxide, monochloramine, ozone and UV light: 4 log removal, provided doses and contact times are sufficient.
Combination of barriers can achieve 6 log removal.
Viruses
Complete removal of human enteric viruses if human waste excluded.
1–2 log removal
Long-term detention
(1–6 months)
Conventional: 2 log removal
Direct: 1 log removal
Membrane: 0 log removal
Chlorine, chlorine dioxide, monochloramine, ozone and UV light: 4 log removal, provided doses and contact times are sufficient.
Combination of barriers can achieve 6 log removal.
Giardia
Complete removal of human infectious Giardia if human and livestock waste excluded.
1.5–2.5 log removal
Long-term detention
(1–6 months)
Conventional: 2.5 - 4 log removal
Direct: 2 - 3.5 log removal
Membrane: 4 log removal
Chlorine, ozone, UV light and chlorine dioxide: 4 log removal provided doses and contact times are sufficient.
Combination of barriers can achieve 5 log removal.
Cryptosporidium
Complete removal of human infectious Cryptosporidium if human and livestock waste excluded.
1–2 log removal
Long-term detention
(1–6 months)
Conventional: 2.5 - 4 log removal
Direct filtration: 2 - 3.5 log removal
Membrane: 4 log removal
Ozone, UV light and chlorine dioxide: 4 log removal provided doses and contact times are sufficient.
Chlorine and chloramines: 0 log removal at doses that can be applied in drinking water.
Combination of barriers can achieve 5 log removal.
ᵃ Achievable LRVs need to be evaluated/ validated on a case-by-case basis (see Box 5.6) ᵇ Based on information provided in Table 5.6 and Information Sheets ISI.3 - ISI.7
ᶜ Using standard technology (catchment control, detention, conventional filtration, disinfection). LRV targets taken from Table 5.5
ᵈ Depending on pore size
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