CT’s water resources continue to be affected by a long-term period of mostly dry conditions. In 2018–19, total inflows to the ACT’s 4 drinking supply reservoirs was 32 gigalitres, the lowest since records began in 1912, and 86% below the long-term average. At the end of June 2019, the ACT’s 4 reservoirs were holding just 57% of the total ACT storage capacity. Over the past 10 years, only 12–17% of the total wastewater produced is recycled in the ACT.
Indicator assessment legend
Environmental condition is healthy across the ACT, OR pressure likely to have negligible impact on environmental condition/human health.
Environmental condition is neither positive or negative and may be variable across the ACT, OR pressure likely to have limited impact on environmental condition/human health.
Environmental condition is under significant stress, OR pressure likely to have significant impact on environmental condition/ human health.
Data is insufficient to make an assessment of status and trends.
Adequate high-quality evidence and high level of consensus
Limited evidence or limited consensus
Evidence and consensus too low to make an assessment
Assessments of status, trends and data quality are not appropriate for the indicator
This indicator examines the availability of water resources in the ACT. For information on aquatic ecosystem health, water quality and river flows see the Water section. Whilst some groundwater is used in the ACT for non-potable water supply, it is a small resource compared with surface water, and current use does not represent a risk to groundwater resources. Therefore, the use and availability of groundwater resources is not included in this indicator.
Water underpins almost every aspect of life and is a vital component for human health and wellbeing as well as the health of the ACT’s landscapes and urban environments. The availability of water is key for residential supply, commercial and industrial activities, and agriculture. Water availability is also essential for supporting the ACT region’s population growth.
The availability of water resources is largely determined by the spatial and temporal variability of rainfall, temperature and evaporation, as well as impacts of land use on catchment hydrology. Stream flows in the ACT are highly variable, with drier conditions punctuated by wet years that replenish water storages and river systems. Extended dry periods, such as the Millennium Drought, can lead to severely reduced surface water flows and storage levels in the ACT. While such conditions may necessitate restrictions on water use, it is important that water is used sustainably at all times to ensure secure levels of water resources prior to dry periods.
In response to the Millennium Drought, the ACT Government enlarged the Cotter Dam to increase water storage capacity for long-term droughts. Climate change is predicted to increase the frequency and severity of droughts and will have consequences for the ACT’s water resources in the future (see Indicator CC2: Impacts of climate change).
Water reuse and recycling, both by households and larger users reduces the need to harvest water from the natural environment. In addition, the volume of wastewater that the community produces is relatively stable, so recycling provides a reliable source of water.
ACT’s urban water supply
The ACT draws water from three separate catchments (Figure HS30):
- the Cotter River Catchment and its three reservoirs Cotter, Bendora and Corin.
- the Queanbeyan River Catchment which supplies Googong Dam in New South Wales (NSW).
- the Murrumbidgee River Catchment, via the Cotter Pumping Station and the Murrumbidgee to Googong water transfer.
Water storages in the ACT have a combined capacity of 278 gigalitres. This includes the Corin (70.8 gigalitres), Bendora (11.4 gigalitres) and Cotter (76.2 gigalitres) storage reservoirs on the Cotter River and the Googong (119.4 gigalitres) storage reservoir on the Queanbeyan River. The Googong reservoir is the largest water supply reservoir and represents 43% of the ACT’s storage capacity.
The ACT sources water from each catchment depending on water availability, water quality, ability to meet demand, operational cost and infrastructure performance. Corin and Bendora reservoirs are the cheapest sources of water in the ACT due to their gravity-fed supply to the Stromlo water treatment plant and cleaner water requiring less treatment.
Water can also be sourced come from:
- Googong Reservoir: this is more expensive because the Googong water treatment plant is supplied from Googong Reservoir via pumps and the water quality from this rural catchment is not as good and requires more expensive treatment.
- Cotter Reservoir: pumping from the Cotter Dam to the Stromlo water treatment plant requires water to be moved to a higher elevation, resulting in higher pumping costs than Googong.
- Water can be pumped from the Murrumbidgee River to Googong Reservoir, but the combination of pumping and treating the poorer water quality from the Murrumbidgee River means that higher costs are incurred.
The use of various water sources in 2018 demonstrates the flexibility of the ACT’s water supply. In response to significantly low rainfall in that year, Cotter Reservoir was used as the main source of supply and was supplemented by Bendora and Googong.
Figure HS30: The ACT’s water supply network
Condition and trends
Water storage volume trends for the 2015–2019 period are presented below. Volumes are determined by inflows from rainfall, evaporation, the volume of water consumed, and spills and releases for environmental flows. This means that changes in the storage volumes of individual reservoirs will be highly variable, regardless of inflows. This is particularly the case for the Cotter catchment reservoirs which are generally the main sources for ACT’s water. For example, during 2018–19, the Cotter catchment reservoirs provided 78% of the water supplied to the ACT and Queanbeyan, of which Bendora reservoir contributed 29% and the Cotter reservoir 49%.
Over the reporting period (2015 to 2019), storage volumes were variable for all ACT reservoirs in response to annual changes to inflows and water use (Figure HS31). However, by June 2019 all reservoirs were at their lowest levels over the 5-year period:
- Corin reservoir fell to 24% (17 gigalitres) of capacity from a reporting period high of 62% in June 2017.
- Bendora reservoir fell to 44% (5.0 gigalitres) of capacity from a reporting period high of 92% in June 2015 and 79% in 2018. Bendora has the lowest total capacity of all the ACT’s reservoirs and shows greater variation in response to inflow and outflow changes.
- Googong reservoir fell to 61% (73 gigalitres) of capacity from a report period high of 100% in June 2015 and 2016, and
- Cotter reservoir retained the highest volume, only falling to 82% (62 gigalitres) of capacity from a reporting period high of 98% in June 2017 and 2018.
Figure HS31: Percentage of storage capacity for ACT reservoirs, June 2015 to June 2019.
At the end of June 2019, the ACT’s four reservoirs were holding 57% (157 gigalitres) of the total ACT storage capacity (Figure HS32). The enlargement of the Cotter Dam in 2013 increased the ACT’s water storage by 72 gigalitres. In the absence of this increase, the combined ACT storages would have been around 30% of their total capacity – similar to levels during the Millennium Drought.
The water storage volumes between 2015 and 2019 are consistent with a long-term trend in reduced storage inflows. Available water resources have declined significantly in the past 20 years, with mean storage volumes 41% below the long-term average (source: Icon Water).
Figure HS32: Total storage volumes for ACT reservoirs, June 2015 to June 2019.
Figure HS33: Total inflows to the ACT’s four water storage reservoirs, 2001–02 to 2018–19.
The Lower Molonglo Water Quality Control Centre (LMWQCC) non-drinking water scheme is the primary supply of non-drinking water in the ACT. Between 2009–10 and 2018–19, there was little variation in the ACT’s wastewater recycling with volumes remaining around 4,000 megalitres to 4,500 megalitres (Figure HS34). This represented around 12% to 17% of the ACT’s total wastewater produced. The remaining treated wastewater from LMWQCC is either reused at the plant or is discharged into the Molonglo River providing environmental flows, protecting riverine ecosystems and providing for downstream use.
Wastewater recycling is largely dependent on the annual demand for such water and can also be affected by periods of high rainfall which can reduce the need for recycled water. There is currently low demand for recycled water in the ACT; however, if drought conditions continue, there may be a growing need for recycled water.