Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Professor Peter W. Newton, CSIRO Building, Construction and Engineering, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06747 7
Liveability: environmental quality (continued)
Water quality (continued)
Waterborne disease is an illness caused by drinking contaminated water. The contamination can be bacteria (Salmonella, Campylobacter, Shigella, Myobacterium, Vibrio, Leptospira, Escherichia coli), viruses, or small parasites (Cryptosporidium, Giardia, Toxoplasma). Most outbreaks of waterborne disease are caused by faecal contamination of water by infected animals or people. Drinking water systems and public swimming pools have both been associated with waterborne disease outbreaks. People who have suppressed immune systems are at greater risk from waterborne disease.
For many years it has been widely accepted that contaminated water is the major vehicle for transmission of diarrhoeal diseases, and this has led to a predominant emphasis on the microbiological quality of drinking water. However, recent work by the World Health Organization and others has shown that food-borne transmission is more important and probably accounts for 70% of diarrhoeal episodes (Cooperative Research Centre for Water Quality and Treatment 1996). Outbreaks of waterborne disease in Australia are thought to be rare, although it is often difficult to determine the source of such diseases. They may be foodborne, faecal-oral, or person to person, as well as waterborne.
Campylobacteriosis, cholera, cryptosporidiosis, leptospirosis, salmonellosis, shigellosis, tuberculosis, typhoid and yersiniosis are nationally notifiable diseases in Australia that may be waterborne; giardia may be waterborne but is not nationally notifiable. The National Notifiable Disease Surveillance System annual reports provide little information on the source of the disease associated with the notification. Therefore, it is not possible to provide an indication of the relative importance of waterborne disease compared to foodborne, faecal-oral, or person to person transmission. In addition, water is often considered a food and so disease caused by contaminated water is reported as 'foodborne'.
Several incidents of confirmed waterborne disease have been reported in recent years. For example, 23 staff on a resort island in north Queensland had confirmed probable cases of campylobacteriosis in May and June 1997. The cause was determined to be due to contamination of a rainwater tank by faeces of wild animals (ADHAC 1999a).
Cryptosporidium constitutes a substantial public health hazard in swimming pools (ADHAC 1998). There were recent outbreaks of cryptosporidiosis in most states of Australia, traced to contaminated public swimming pools (ADHAC 1998; Swinton 1999).
In the Sydney event of July and August 1998, despite the erratic counts (of C. parvum) in the water supply, there was no disease attributed to the water (ADHAC 1999b, Swinton 1999). A number of questions remain unanswered in relation to the Sydney incident: Was the strain of C. parvum that was counted a non-infective strain? Were the wildly erratic analytical results correct? Or was the population sufficiently auto-immunised?
It is extremely difficult to monitor outbreaks of Cryptosporidium, since the incubation period after exposure is 6-7 days, followed by diarrhoea containing thousands of oocysts. Testing of the stools of severely affected patients does not usually occur for another 4-10 days, with further delay in reporting of 3-4 days (Swinton 1999). At present there are considerable variations in testing practices and reporting procedures between different states and territories, which makes it difficult to establish a comprehensive picture (ADHAC 1999b). As detection methods for C. parvum improve, the frequency of detection increases. However, we have no previous data to say whether there is an increasing trend, particularly as the background of gastroenteritis from food will mask all but a major waterborne outbreak (Swinton 1999).
The CRC for Water Quality and Treatment has recently completed a three-year study on the relationship between human health and water quality (AWWA 2000c). The study concluded that it is unlikely that Melbourne would derive a health benefit from filtering drinking water from its highly protected catchments. As found in Sydney during 1998, the health implications of applying ever-more sophisticated testing methods cannot always be determined. The study director, Professor Kit Fairley, considers the study a valuable tool in deciding whether contributing significant amounts of money to increase the degree of water treatment is justified, when there would not be any measurable benefits to human health (AWWA 2000c). The results of the study reinforce the Productivity Commission report on setting water quality standards in Australia, which stated that health benefits are rarely weighed up against the cost to the consumer when developing standards (AWWA 2000c).
If biological contamination of Australia's drinking water is rare, salinity is a much more pervasive problem, especially for cities and towns that draw water from inland rivers and groundwater aquifers (e.g. Dubbo in New South Wales, Katanning in Western Australia). For Adelaide in particular salinity represents a real challenge. Figure 75 summarises current Adelaide water use. On average the SA Water Corporation supplies 176 GL per annum to the Adelaide metropolitan area. The split between supply from the River Murray and the Adelaide Hills is 40:60 in an average year and 90:10 in dry years.
Figure 75: Average water use in the Adelaide metropolitan area.
The recent salinity audit for the River Murray System (Murray-Darling Basin Ministerial Council (MDBMC) 1999) reports that, by 2020, water supplied to Adelaide will exceed the World Health Organisation threshold (upper limit 800 EC) for drinking water 20% of the time, and by 2050, 50% of the time. Table 56 shows estimated average salinity in the River Murray in South Australia. The current impact cost of salinity on irrigation areas and urban areas is estimated to be $46 million per annum (MDBMC 1999).
|Site||Average river salinity (EC)A|
AEC is electrical conductivity (measured as microsiemens per centimetre or 1 EC unit to mg/L of total dissolved salts, a multiplication factor of 0.6 generally applies.
BMorgan is used by the MDBMC as the key indicator site for monitoring and predicting salinity trends; it is upstream of the major off-takes of water to Adelaide.
Source: MDBMC (1999).
An economically and technically efficient solution to this problem in Adelaide has been advanced by CSIRO, the aim of which is to eliminate the need for Adelaide to source water from the River Murray (CSIRO 2000). Figure 76 summarises the extent of savings that might flow from the introduction of demand management, installing low-volume water appliances, replacing sewerage infrastructure with smaller scale plants, stormwater capture and use, aquifer recharge, using smaller pipes and levelling the peak loads on the supply system, and managing externalities sensitively.
Figure 76: An optimistic model for water use in the Adelaide metropolitan area for an average year assuming a 30% reduction in aggregate water use from 176 GL per year to 123 GL.
One challenge in achieving this vision is the need to manage increasing levels of salinity detected in some Adelaide Hills catchments. Salt concentrations in several of these catchments already periodically exceed Australian drinking water guidelines (Jolly et al. 2000).
Fluoride is a naturally occurring element found in soil, water and plants. Sodium fluoride is routinely added to drinking water supplies in the capital cities in Australia, with the exception of Brisbane, usually as one per million parts for its proven ability to reduce tooth decay and gum disease by up to 70% (NHMRC 1999). In addition to Brisbane, there are several other regional centres (e.g. Geelong, Ballarat, Sale, Latrobe Valley, Gosford) without fluoridation. Debate continues in epidemiological circles in relation to the pros and cons from a health perspective - although the weight of evidence seems to favour benefits. From a social equity perspective, fluoridation is seen as being of particular benefit to socially disadvantaged groups who have the highest rates of tooth decay and have less access to dental services.
Most of the Australian population has access to reticulated water supply and wastewater services, although the standard of service received does vary for location to location, with remote communities typically receiving a lower standard of service. In locations receiving a lower level of service, there is a shift towards the use of small-scale (and in some cases on-site) infrastructure because of the potentially high costs of providing the traditional large-scale centralised infrastructure. There is increasing interest in alternative methods of providing water services.
The Sydney 'boil water' alerts in 1998 and the failure of the Adelaide wastewater system in 1997 have highlighted the fragile nature of urban water infrastructure in Australia and the scale of the impact that a system failure can have on an urban area. Adelaide, amongst other urban centres, also faces the challenge of rising salinity levels in drinking water sources. So most, but not all, Australians receive a high level of water supply and wastewater service, although maintaining this current level of service in the face of ageing infrastructure is placing a financial burden on the water industry.