A1.2 Water supply system analysis

Assessment of the drinking water system provides an important information base and is a prerequisite for subsequent steps in which strategies for prevention and control of hazards are planned and implemented. The purpose of this element is to develop a broad overview and basic understanding of the water supply system. It is not intended to be an extensive data collection exercise; rather, it is the characterisation of the system at an appropriate level of detail to provide a useful information base from which to make effective decisions.

Summary of actions

• Assemble a team with appropriate knowledge and expertise.

• Construct a flow diagram of the water supply system from catchment to consumer.

• Assemble pertinent information and document key characteristics of the water supply system to be considered (see Table A1).

• Periodically review the water supply system analysis.

Characterisation of the water supply system should be fully documented and should be a collaborative effort between relevant agencies. Characterisations will be specific for each system but should include, where appropriate, consideration of the catchment area, source water, groundwater system, reservoirs and raw water transport, treatment systems, distribution system and consumers.

Table A1.1 provides examples of some key characteristics to be considered in assessing drinking water supply systems from catchment to consumer. Seasonal characteristics, as well as extreme and infrequent events such as droughts or floods, should also be considered.

Much of the necessary information may be available in existing documentation from studies carried out previously or from external agencies. Sources of useful information can include:

• land use surveys and catchment maps

• sanitary surveys and/or vulnerability classifications and microbial band allocations as used for microbial health-based target determination

• surveys of major streams and rivers

• research and investigative monitoring

• inspections and field audits

• employee knowledge

• records from local authorities (e.g. locations of septic tanks, animal feedlots, sewage treatment plants)

• community surveys

• public and consumer complaints.

Geographic information systems (GIS) can provide a useful means of displaying, cataloguing and interpreting data.

Table A1.1 Key characteristics of the drinking water supply system

Catchments	Catchments (continued)
Geology and soils Topography and drainage patterns (hydrology) Streams and rivers Meteorology and weather patterns (climatic and seasonal variations) Riparian conditions Vegetative cover General catchment and river health Wildlife (e.g. native and feral animals) Historical contaminated sites Competing water uses Land irrigation practices	Nature and intensity of development and land-use activities: agricultural, dairy and animal husbandry land clearing forestry mining industrial rural and urban development / residential sewage treatment works and septic tanks recreational activity Intermittent or seasonal use practices Future planning activities Development and planning restrictions

Source water	Source water (continued)
Surface water (river, reservoir, dam) Groundwater Flow and reliability of source water Seasonal and event changes (including infrequent events such as droughts or floods) Spatial variations	General and unique constituents (physical, chemical, microbial): major ions and pH salinity, hardness turbidity bacteria, viruses and protozoa naturally occurring organics volatile and nonvolatile synthetic organics metals and radionuclides

Groundwater systems	Groundwater systems (continued)
Geology, homogeneity Confined or unconfined aquifer Depth to water table Flow rate and direction	Dilution characteristics Recharge area Well-head protection Depth of casing

Storage reservoirs and intakes	Storage reservoirs and intakes (continued)
Detention times Reservoir design: size materials storage capacity depth of storage Seasonal variations: stratification algal blooms	Treatment efficiencies (microbial removal) Protection (e.g. covers, enclosures, access) Recreational or human activity Intake location and operation Bulk transport: pipeline material length flow rate and changes in flow rate cleaning systems

Treatment systems	Treatment systems (continued)
Treatment processes (including optional processes) Treatment configuration Equipment design: size materials peak flow rates process change control backup systems Monitoring equipment and automation	Water treatment chemicals used: coagulant filtration aids fluoride powdered activated carbon disinfectant Treatment efficiencies Disinfection log removals of pathogens Disinfection residual and contact period

Service reservoirs and distribution systems	Service reservoirs and distribution systems (continued)
Reservoir design: size materials storage capacity depth of storage Detention times Seasonal variations: stratification Protection (e.g. covers, enclosures, access)	Distribution system design: size network pipe materials pipe age Hydraulic conditions (e.g. detention times, flows) Backflow protection Secondary disinfection practices Disinfectant residuals Disinfection byproducts

Consumers	Consumers (continued)
Consumer distribution (industry, bodies corporate, general community) Vulnerable groups (hospitals, nursing homes)	Water demand and patterns of drinking water consumption (diurnal and seasonal variations) Internal plumbing