Perth weekly water update - 30 July 2021
| Target | Actual | |
|---|---|---|
| July water use to date |
17.8 billion litres |
18.8 billion litres |
| Dam storage levels | N/A | 51.6% |
| Monthly streamflow into dams | N/A | 35.07 billion litres |
| July rainfall to date | 167.70 mm (July average rainfall 1876-2016) | 265.20 mm |
| Note: 1 billion litres = approximately 400 Olympic swimming pools. Please note the figures in this table are rounded (except for rainfall) to the nearest whole number. | ||
Water use
Average water use over the past week was 613 million litres per day – above the demand forecast of 586 million litres per day.
Daily water use for the last 5 days
| Date | Actual water use (million litres) | Forecast water use (million litres) |
|---|---|---|
| 30/07/2021 | 627 | 584 |
| 29/07/2021 | 601 | 584 |
| 28/07/2021 | 608 | 584 |
| 27/07/2021 | 610 | 584 |
| 26/07/2021 | 657 | 588 |
| Note, water use is calculated up to 8am each day for the previous 24 hour period. | ||
Since 1 July 2021, we have used 18.02 billion litres of water – which is 0.76 billion litres above the forecast target for this period.
Dam levels (total for 15 dams)
The dam storage levels are slightly up on last week and are sitting at a combined 51.6 per cent* of full capacity.
*Please note some dams are filled from different sources - dam levels include the transfer of groundwater and desalinated seawater from treatment plants as well as streamflow (that comes from rainfall). As we use many different sources of water, dams are no longer an accurate indicator of the health of Perth's overall water supply situation.
Streamflow (total for 15 dams)
From 1 May 2021, the dams have received 37.6 billion litres of streamflow. The post-1975 average for the May to April period (called the streamflow year) is 175.59 billion litres.
Sprinkler roster compliance
From 1 January to 9 July 2021, we have taken a total of 3,997 actions (warnings + fines) compared with 3,767 actions for the same period in 2020.
Annual rainfall
Perth has received 592.4 mm of rainfall since 1 January 2021. The average (1876-2016) rainfall for the same period to the end of July is 543.6mm.
General water news
Perth has received a drenching this July, with 265.2mm of rain received in 30 days and only one day left to go. While the Bureau of Meteorology forecasts more rain tonight and tomorrow, it’s still yet to be seen whether we’ll pass the record of 278mm received in July 1995.
The heavy rainfall received this month has also sparked the curiosity of many Western Australians who have asked about metro dam levels, and whether it’s made any difference.
In July so far, we have received 35.07 billion litres of water into our dams (through streamflow). As a point of reference, 1 billion litres is roughly the volume of water needed to supply customers in Perth (and those along the Golden Pipeline) with water for a single summer day.
While this may seem like a decent amount, our average annual streamflow figure 40 years ago was 420 billion litres. In 2020-21, it was 42.5 billion litres – that’s an 80% reduction in just a few decades.
Today, streamflow into dams accounts for just 15% of Perth’s water supply needs. As we can no longer rely on the rainfall we once received to fill our dams, we’ve had to diversify with climate-independent sources such as seawater desalination (43%), groundwater (39%) and water recycling (3%).
Dams still have an important role to play in collecting available streamflow, however, they’re now used primarily as reservoirs to store desalinated water and groundwater, ready for when we need it most during the warmer months.
So, while the recent rain is very welcome, it doesn’t mean we can become complacent when it comes to being waterwise. To ensure the future of water in WA, everyone must to do their bit to conserve our precious water – by adhering to the watering restrictions and being mindful of their water use.