Metro weekly water update - 17 August 2018

Note: 1 billion litres = approx. 400 Olympic swimming pools.  Please note these figures are rounded (except for rainfall) to the nearest whole number.

Water use

Average daily water use over the last week was 642 million litres, which was above the forecast of 542 million litres.  So far, in total this financial year, we have used 28 billion litres of water - this is one billion litres above what we had forecast.

Dam levels

Perth’s dam storage levels have increased by 18 billion litres over the last seven days and are now at 56% of full capacity.   Please note our dams store water from three different sources and this increase may be due to groundwater and desalinated seawater transferred from treatment plants as well as streamflow (produced by rainfall).

Streamflow (total for the metro’s 15 dams)

From 1 May 2018 to 16 August 2018 the dams received 83 billion litres of streamflow.  From 1 May 2017 to 17 August 2017 the dams had received an estimated 49 billion litres of streamflow.    The post 1975 average for the May to August period is 107 billion litres.

Sprinkler roster compliance

The Winter Sprinkler Switch-off now applies, and our inspectors issued 102 warnings and 9 fines this week.  Since 1 January 2018, we have taken a total of 5821 actions (warnings + fines) compared with 6904 actions for the same period in 2017.

Annual rainfall

Perth has received 616.6 mm of rainfall since January this year.  According to updated figures released by the Bureau of Meteorology the cumulative mean rainfall (1994-2017) for the Perth metro for January to December is 732.8 mm.  The 1876-2016 annual average is 838.9 mm.

General water news

This week we have been contacted by media in Australia’s eastern states comparing Perth’s water situation to drought-stricken New South Wales.

Unlike some states on the east coast, there is no dam level trigger to switch our desalination plants on or off. To provide half of Perth’s water, desalination plants are run at close to full capacity for the entire year. Our two desalination plants have been producing water due to low dam levels since they began operating.

We monitor the water supply situation throughout the year and carry out a review at the end of each winter, to determine how much water can be sourced from dams and groundwater, or produced by desalination and groundwater replenishment for the coming year and beyond.

Our first priority will always be providing a secure water supply in the long term, and using climate independent sources such as desalination helps provides a buffer for the drier winters.

Desalinated water is more expensive to produce than taking water from our dams through streamflow, and this is always taken into account when balancing the source mix to ensure we can supply enough water each year in the most efficient way.

The total unit cost of desalinated seawater, taking into consideration operating and capital costs, is around $2 to $3 per kilolitre. This is compared to dam water which is around 40 cents per kilolitre.