The average rainfall in Sydney from 1913 to 1998 was 1,203 mm/year [15]. The year is sub-divided into quarters that approximately follow the seasons: Q1 from November to January; Q2 from February to April; Q3 from May to July; and Q4 from August to October. The wettest period of the year is generally in the second quarter (Q2) while the driest is the fourth quarter (Q4). The average quarterly and yearly rainfall patterns over the study period (2002 to 2009) vary greatly from year to year. The driest year was 2005 with a total annual rainfall of only 808 mm and the wettest year was 2007 with 1,325 mm of rainfall. In fact 2005 was the third hottest summer recorded in NSW [16]. Some notable phases during the study period include the fourth quarter of 2002 (Q4-2002) and first quarter of 2003 (Q1-2003) where a total of only 47 mm and 120 mm of rainfall occurred respectively; and the third quarter of 2007 (Q3-2007) where a total of 588 mm of rainfall occurred. This was almost three quarters of the total rainfall that occurred in 2005 and well above the quarterly average.

High average temperatures can be a leading factor for increased water consumption due to the need for additional watering of gardens and lawns and higher overall consumption. The quarterly average temperatures were 25.6 °C (Q1), 25.2 °C (Q2), 19.1 °C (Q3), 21.7 °C (Q4), and the annual average was 22.9 °C. The hottest part of the year is generally in the first and second quarter (November through to April) while the coldest part of the year is the third quarter (May through to July).

SWC implemented various water restrictions over the past decade due to the declining water levels in dams that supply the Sydney metropolitan area [17]. Voluntary restriction commenced in Sydney in October 2002. SWC introduced Level 1 restrictions in October 2003 when dam levels dropped below 60% [17]. Dam levels continued to decline due to the lack of rainfall in the dams’ catchment and by June 2004 were below 50% when SWC implemented Level 2 restrictions [17]. In June 2005 the dam levels had dropped further to below 40%, resulting in Level 3 restrictions [17]. Level 3 restrictions remained in place for a number of years. In June 2008, SWC eased Level 3 restrictions to permit its residential customers to wash cars, boats and caravans at home as well as to clean the windows and walls of their house with a hose as long as a trigger nozzle was fitted. By June 2009 water levels in the dam had been steady at around 60% for 12 months. Level 3 restrictions ceased and SWC brought in new “Water Wise Rules” [17] which are still in effect despite dam water levels currently at 100%.

In October 2002, SWC introduced a rainwater tank rebate scheme in an effort to promote the installation of rainwater tanks so that water consumption could be better managed. The scheme provided various rebates (monetary refunds) for their installation. USD 150 was provided for the installation of rainwater tanks with a capacity of between 2,000 to 3,999 L, USD 400 for 4,000 to 6,999 L and USD 500 for more than 7,000 L. Additionally, further monetary incentives (USD 150) were provided to connect the rainwater tank to the household toilet system and/or laundry systems. This rose to USD 300 from October 2006. In July 2007, USD 500 was given for a rainwater tank connected to the household toilet system and/or USD 500 to the laundry systems. This scheme ended in June 2011.

SWC supplies water to properties located in Sydney’s metropolitan area. A database of water bills, which are issued quarterly and include the amount of water used at a property, was used to undertake a statistical analysis of residential water usage in Sydney. The database covered the period spanning from November 2001 (Q1-02) to October 2009 (Q4-09). The quarters approximately follow the seasons: Q1 from November to January; Q2 from February to April; Q3 from May to July; and Q4 from August to October. The first quarter in the dataset (Q1) covered the period November 2001 to February 2002. The total number of properties in the database totalled 1,207,359 of which 962,697 were categorised as “Residential - Single Dwelling”. By 2009, a total of 52,576 households had registered for a rainwater tank rebate with SWC which represented a 5.5% of all residential single dwellings supplied by SWC. The average quarterly consumption for these properties with and without rainwater tanks for each Local Government Authority (LGA) was provided. Data was released in this restricted form to comply with SWC’s privacy restrictions which prohibits releasing any information pertaining to their individual customers.

The SWC database covers a large data set of various property types, land sizes and water usages. A subset was created - Conditional Data Set - Residential properties (CDSR) - to remove data not used in this study. The CDSR was separated into individual LGAs to provide a location-based investigation and further isolated properties to the following conditions: single dwelling residential properties only; properties with a lot area greater than 100 m² and no larger than 2,000 m² as larger properties are not typically urban residential; and properties with typical water usage between 10 kL to 500 kL per quarter (typically 100 L to 5,000 L per day). Subsequent to creating the CDSR, a second data set was created with these same conditions except it included only those properties with a registered rainwater tank rebate (CDSRT).

The CDSRT had to be standardised to ensure that the data set was consistent to make it possible to compare water usage before and after a rainwater tank had been installed. To standardise the data, individual LGA CDSR were graphed to observe the water usage trend over the study period (Q1-02 to Q4-09). The trend in the data was due to the impact of factors that led to changes in water usage other than the rainwater tank. These factors include the effects of SWC’s restrictions on water usage, seasonal and climate variations, and the changes in consumers’ water usage patterns (e.g. as a result of public education campaigns).

The CDSR data was grouped by LGAs. For each LGA a factor was determined for the average water usage for each quarter relative to the average of each LGAs water usage over the study period (Q1-02 to Q4-09). Subsequently, these factors were applied to the respective individual quarterly water bills of the CDSRT to remove the impact of factors other than the installation and use of rainwater tanks. The data set with factors applied is called the Standardised Conditional Data Set with Rainwater Tanks (S-CDSRT). The outcome of applying the factors to the CDSRT allowed a comparison between water usage, before and after the rainwater tanks were installed with any of the other effects discussed above removed. For a particular house, the plot of S-CDSRT water consumption data would show a sudden drop in the quarter when the rainwater tank was installed. The drop in water consumption before and after installation is reduction in water consumption due to the installation and use of rainwater tanks. The reduction in water consumption was calculated for rainwater tanks over a period of at least two years (8 quarters) before and at least two years after the installation. There were 32,276 properties with rainwater tanks or 61.4% of the total number of properties with rainwater tanks meeting this criterion. The proportion of rainwater tanks meeting this criterion was over 50% in all but 6 LGAs. Any decline in the average water usage trend after the installation of the rainwater tank would confirm that it led to a reduction in potable water usage.

Figure 1 shows the reduction in water consumption in Sydney and in various LGAs over the period leading up to and including the water restrictions. The overall trend in the data in terms of the times when water consumption rises, falls and plateaus is similar. Water consumption sharply fell during the period of voluntary restriction and reflects: firstly, the community education and publicity campaign to save water; and secondly, the falling of dam storage to critical levels over that period that heightened community concern in that period. The initial saving was so large that the reduction in water consumption level during periods of level 1, 2 and 3 restrictions actually levelled off even when they became increasingly severe. Savings in water consumption became harder to achieve once practices and habits in the community that were easier to change were accomplished. The average reduction in water consumption from 2002 to 2009 was about 24%. Not all the saving in water consumption can be attributed to the water restrictions program. Concurrently, during this period other measures were implemented to reduce water consumption. This included the installation of water savings devices such as water efficient shower heads and dual flush toilets, and implementing the Building Sustainability Index (BASIX) for new and refurbished buildings which aimed to deliver effective water reductions in Sydney and across New South Wales. BASIX is a planning initiative of the New South Wales State Government that requires all new dwellings to be designed and built to achieve a 40% reduction in water consumption and 40% reduction in greenhouse gas emissions compared to the average dwelling. Another objective was to continually replace water appliances with new and more efficient ones.

Figure 1.

Variation in average water consumption in Sydney and its LGAs

Figure 1 shows the variation in water demand in Campbelltown and Hornsby which have the lowest and highest rainfall, respectively. The annual rainfall in Hornsby is approximately double that in Campbelltown. Both suburbs are similar in character with predominantly single dwelling houses and large gardens. Income levels in both suburbs are also similar and reasonably close to the Australian average [18]. While the difference in water consumption between the two LGAs is not large (< 5%), Hornsby had a slightly lower consumption. The plot also shows the LGAs with the largest (Ku-ring-gai) and smallest (Auburn) reduction in water consumption during the water restrictions period. The former is a wealthy leafy suburb with predominantly single dwelling houses with large gardens while Auburn is a suburb located near the geographical centre of Sydney (20 km from the CBD) with mainly smaller lot areas and smaller outdoor/garden areas. While there was a tangible reduction in both suburbs, the reduction in Ku-ring-gai was substantial. Both Ku-ring-gai and Auburn had similar water consumption patterns at the end of the monitoring period and this was about 10% larger than the Sydney average.

Figures 2–5 present an overview of water consumption in Sydney together with various socio-economic indicators which were prepared from the SWC database together with data from the Australian Bureau of Statistic [19], and the Bureau of Meteorology [15]. The data across Sydney is presented by LGAs. For clarity, the overarching map containing most of the LGAs is referred to as the ‘outer Sydney area’ and the smaller insert is referred to as the ‘inner Sydney area’.

Figure 2.

Water consumption for single households in the Sydney metropolitan area

The SWC data shows an overall decline in the average annual water consumption per household in Sydney’s metropolitan area during the study period (Q1-02 to Q4-09) from 282 kL/year in 2002 to 200 kL/year in 2009. Even without including the impact of rainwater tanks (discussed in the next section) the overall average water consumption fell by 24% over the study period. Table 1 summarises the reduction in water savings in all 44 LGAs. These reductions can be attributed to effective demand management techniques such as the Sydney-wide water restrictions between 2003 and 2009 [20] and the introduction of water efficient fixtures like taps, dual flush toilets and efficient shower heads. SWC installed these free of charge or at subsidised prices. Other factors included the implementation of BASIX for new and refurbished buildings, and the installation of new water efficient appliances. It may also be due to lot sizes becoming smaller in part due to sub-division of existing residential lots which leads to smaller gardens [21].

When comparing the reduction in the level of water consumption between the various LGAs (Figure 2a) it is evident that water reductions are smaller for properties with smaller lot areas (Figure 3a). The majority of LGAs in inner Sydney which have small lot areas had about 20% to less than 20% reductions in water usage. Most of the LGAs in the outer Sydney area with some exceptions (Liverpool, Fairfield, Holroyd, Parramatta, Auburn and Blacktown), had significant reductions, most of which were greater than 28%.

Figure 3.

Average single dwelling property area and average number of persons per household in Sydney, data from Australian Bureau of Statistic [18], [19]

A relationship exists between the water consumption in terms of per capita daily demand (L/person/day) compared to the number of people per household [22], [23]. Figure 3b shows that as the number of people per household increases, water consumption (in per capita terms) (Figure 2b) generally decreases (p = 1.7E⁻⁴¹ < 0.05). This is true for most LGAs in the inner Sydney area (except Leichardt and Marrickville) which have less people per household and higher per capita usage compared to most LGAs in the outer Sydney area (except Pittwater, Baulkham Hills, Hawkesbury, Wollongong and Sutherland). These areas have more people per household and lower per capita usage. The trend between water consumption is not completely explained by the house lot area and number of people per household. Socio-economic factors may be considered and they are explored in more detail below to assess their impact on water consumption.

Figure 4 (a-d) shows the distribution of socio-economic aspects such as levels of educational qualifications, mean taxable incomes, portion of rental properties and portion of residents born in Non-English-Speaking Countries (NESC) [24].

Figure 4.

Socio economic indicators in the Sydney metropolitan area, data from Australian Bureau of Statistic [18]-[19]

Table 1 also provides the percentage of water savings by installing rainwater tanks. The average distribution of reduction in water savings across all 44 LGAs is 9% ± 1.9%. The statistical significance in the reduction of the mean water usage is extremely small (p = 1.9E⁻¹⁴³ < 0.05) due to the very large data set of properties on the SWC database. On average a household could save around 24 kL of water annually by installing a rainwater tank. This level of savings was compared to the findings of other studies undertaken on individual LGAs in Sydney’s metropolitan area and surrounding LGAs that received SWC water. Moy [8] revealed households that installed rainwater tanks in Wollongong and Shellharbour reduced their water consumption by approximately 10.3% although this data was not adjusted for the overall reduction of water consumption that occurred in the wider community. Furthermore the reduction in water consumption was not individually reported for Wollongong LGA and Shellharbour LGA. Table 1 shows the reduction in water consumption due to rainwater tanks for Wollongong and Shellharbour was 7% and 8%, respectively in this study.

Knights et al. [9] presented data from the rainwater tank incentive scheme in Marrickville LGA indicating that rainwater tanks could reduce residential water consumption on average by 25%. Again this data was not adjusted for the overall reduction of water consumption that occurred in the wider community. A comparison of the methods of analysis between the studies is difficult without knowing the full extent of the data sets selected and whether specific conditions were placed on removing any data (e.g. as was carried out in this study, and outlined in the ‘SWC Database’ section of this paper).

Figure 5a shows the level of uptake of the rainwater tank rebate in LGAs, and demonstrates that the largest adopters were Wollongong, Wollondilly and the Blue Mountains in the outer Sydney area, and Botany Bay in the inner Sydney area, with more than 10% of houses having received a rainwater tank rebate. Other outer Sydney LGAs with high levels (5 to 10%) were Sutherland, Camden and Penrith, along with all northern LGAs from the Hawkesbury through to Pittwater and the inner Sydney LGAs of Hunters Hill, Lane Cove, Willoughby and Mosman. The remaining inner Sydney areas were evenly split between lower uptakes of 3 to 5% or less than 3%. This could be due to the general lack of space for a rainwater tank in residential backyards in the inner Sydney locations (Figure 3a). Also a higher proportion of the houses were rented compared to the outer Sydney LGAs (Figure 4c). LGAs located in the outer Sydney area with more people born in NESC had lower levels of rainwater rebate uptake (between 3 to 5% or less than 3%).

Figure 5.

Average percentages of water savings from rebated rainwater tanks in the Sydney

Figure 5b shows the level of reduction in water consumption attributable only to installed rainwater tanks. The reduction in water consumption was calculated for rainwater tanks over a period of at least two years before and at least two years after their installation. The results indicate that most properties within inner Sydney with a rainwater tank achieved at least a 9 to 11% additional reduction in water usage, with more than half of those LGAs achieving more than 11% additional reductions. These same levels of water usage reductions were also observed for most of the northern and central LGAs in the outer Sydney area.

A reason for this large reduction in water consumption in the inner Sydney LGAs as compared to southern and western outer Sydney LGAs (Figure 5b), could be explained by the smaller lot areas (Figure 3a) in the former. It is estimated that the sizes of the rainwater tanks would not differ all too much in inner and outer Sydney LGAs, as compared to the difference in lot sizes. In inner Sydney LGAs, there would be a higher yield of collected rainwater relative to the area of garden. A rainwater tank in the inner Sydney LGAs would likely contain enough yield for most if not all outdoor watering requirements, and perhaps completely replace the potable water needed for outdoor/garden use. In outer Sydney LGAs, with much larger outdoor and/or garden areas, rainwater can only supplement potable water supplies rather than replace it.