Impact of Demographic Change and Urban Consolidation on Domestic Water Use
Published: June 2005
Water Services Association of Australia Inc
Authors
- Bob Birrell , Director, Centre for Population and Urban Research, Monash University
- Virgina Rapson, Research Manager, Centre for Population and Urban Research Monash University
- T. Fred Smith, Honorary Professorial Fellow, Centre for Population Research, Monash University
Description
The purpose of this report is to estimate, in the absence of other changes, the impact of demographic change and urban consolidation (where an increased share of the dwelling stock is in the form of medium and high density housing) on domestic water consumption.
Information from the various water authorities was gathered on current (1998-99 to 2003-04) domestic water consumption levels for Melbourne, Sydney, Greater Brisbane*, Adelaide and Perth. This information included an estimate of the percentage of domestic water used outdoors in each city. Using this and other water usage data provided by Melbourne"s Yarra Valley Water, consumption levels were determined for outdoor use by different garden sizes and for indoor use based on the average number of persons per household in each city. For the purpose of the study, it was assumed that there would be no change in these consumption levels over the 2001 to 2031 period.
Water consumption projections were based on four scenarios as follows:
- Scenario A assumes that per capita consumption remains stable at the 2001 rate for each city over the projection period. The 2001 per capita rates vary from between 82 KL/Y for Melbourne to 118 KL/Y for Perth.
- Scenario B is built around projections of household numbers by age and family type for each city. It assumes that these households will continue to occupy the same housing type as they did in 2001. The implication is that the proportion of the dwelling stock which is low-density housing will be maintained in each city.
- Scenario C examines the consequences for domestic water consumption should the dwellings constructed over the next thirty years echo the types of new dwellings built over the 1991 to 2001 decade. The projected households are assumed to adapt to the resulting dwelling stock (as is also the case under Scenario D).
- Scenario D explores the implications for domestic water consumption should the urban consolidation measures of State planning authorities be successful.
Projections for domestic water demand are detailed for each city. The following table summarises these projections.
| Projected increase in water demand, Scenario A compared with other scenarios, five metropolitan areas, 2001-2031 |
||
|
Increase in water demand based on population growth (Scenario A) | Increase in water demand based on population growth, household formation and urban consolidation (Scenarios B, C and D) | |
| Sydney | 33% |
35 to 43% |
|
Melbourne | 33% | 37 to 42% |
| Brisbane |
58% | 62 to 73% |
| Adelaide | 13% |
18 to 20% |
|
Perth | 48% | 53 to 62% |
Population growth is the main driver of increases in domestic water consumption in each city. However, in each case, when household change is taken into account, projected water demand is considerably higher than is the case if demand projections are based just on population growth. This is because, as average household size decreases, average per capita water use within households increases. For example, in the case of Melbourne, the increase in water demand projected on the basis of population growth and a continuation of current per capita consumption levels is 33 per cent. Projections based on population growth, together with household change, indicate a 42 per cent increase in demand.
The changes in the dwelling stock over the projected period to 2031 considered in scenario C would reduce the projected domestic water consumption in each city relative to the consumption projected under scenario B, which only takes account of household change. This is largely because of the drop in the projected proportion of dwellings with large gardens - or any garden at all - consequent on an increased share of the housing stock being in the form of medium to high density dwellings. In the case of Melbourne, should the Victorian Government achieve its aspirations for urban consolidation, the projected growth in domestic water consumption between 2001 and 2031 will be 37 per cent. If the 1990s pattern of dwelling construction continues, domestic water consumption is projected to grow by 40 per cent over the same period.
This pattern is similar in the other cities, except for Adelaide where the impact on domestic water consumption due to changes in the dwelling stock is limited. This is because of the anticipated low rate of population growth, and thus dwelling construction, in the city. In the rapidly growing cities of Brisbane and Perth, urban consolidation (if the planning authorities" aspirations are met) will have a considerable impact on the dwelling stock and will lead to a lower domestic demand relative to the household change scenario. However, it will still leave domestic water demand at levels well above those that would be the case if per capita use in 2031 was the same as in 2001.
In the absence of any other changes, each city faces a much larger demand on its water supply system than would be anticipated if demand projections are based simply on population growth. For this reason, water utilities should examine the implications of population growth and household changes when projecting future water demand and re-assess their current projections in this context.
* The Brisbane Statistical Division takes in Brisbane City, Beaudesert Shire Part A, Caboolture Shire Part A, Gold Coast City Part A, Ipswich City (Part BSD), Logan City, Pine Rivers Shire, Redcliffe City and Redland Shire
Availability
Publication available from
- Water Services Association of Australia
- 469 Latrobe Street Melbourne 3000
- Telephone: 03 606 0678
- Fax: 03 96060376
- Email: info@wsaa.asn.au