How our water data is updated
We source our rainfall figures for the Perth metro area directly from the Bureau of Meteorology’s (BoM) Perth weather station and update our website daily, when possible.
How often is data updated?
Updated daily - Metro dam volumes, rainfall and water use
Updated weekly - Streamflow
Updated when new data is provided - Regional dam levels – a number of regional dam levels are recorded manually by our teams every 2–3 days. Please note that sometimes circumstances prevent levels from being read, so there may be periods when data is unavailable.
Please note: due to a range of factors, there may occasionally be differences between our data and what’s shown on the BoM website.
Rainfall data updates
We obtain our rainfall figures for the Perth metro area directly from the Bureau of Meteorology’s (BoM), using their Perth Metro weather station (Station ID: 009225)
Daily rainfall updates
- The Bureau of Meteorology (BoM) has been the rainfall data supplier since 1994.
- We check the BoM’s public data every day and update our records when new information is available.
- BoM may revise rainfall information at any time.
- These changes may not show up on our site right away.
- If needed, separate updates may be applied to match revised BoM records.
- These updates may take a little time as revised information becomes available.
- For the most up-to-date readings, please refer back to the Bureau of Meteorology website.
- BoM also explains how they check the quality of their rainfall data and any disclaimers about using it.
Monthly and annual rainfall
- Monthly averages are provided by the WA Climate Services Centre at the BoM Perth Office.
- Annual rainfall figures are sent to us by BoM each January and then published on our website.
Streamflow data updates
Streamflow is the amount of water flowing into our dams from catchments. It’s estimated using a water balance model developed in the 1980s and updated in 2012.
The streamflow data provides monthly streamflow totals for all dams that are part of the Integrated Water Supply Scheme (IWSS). This data helps track how much water is entering our storage systems over time and is a key indicator of water availability.
- We estimate streamflow every Thursday morning using a water balance model.
- The model checks dam levels, rainfall, and other data.
- Final numbers are double-checked monthly by our team.
- We upload the data to our system and website every week.
Please note: Streamflow figures on our website may change throughout Thursday and are considered accurate after 5pm.
Did you know?
More rain doesn't always mean more water in our dams.
Catchments need steady, soaking rain to generate streamflow. Even with above-average rainfall in some areas, poor catchment conditions can result in low streamflow.
Water use data updates
We measure how much water people are using across Perth and nearby areas. This data is updated every day using our internal systems and reflects the total volume of water distributed through our network not the exact amount used by customers.
More detailed information about water supply and consumption is available in our annual report.
Sometimes we may experience technical difficulties with collecting the data, or we may not have usable readings come through from our teams in the field.
For example, if a dam does not have a reading recorded for a specific date, we will not have data to compare it to the same date last year.
We aim high when it comes to the accuracy of our data but sometimes errors can happen so occasionally we will update historical data.
Our dam level data comes from each of our dams. Our larger dams all have a device that daily measures the volume in each dam. Our smaller dams have a measurement graph painted on the wall of the dam from which our teams take a physical reading each week.
We report metro dam levels to one decimal place now due to the uncertainty in total dam volumes being greater than 0.4-0.5 gigalitres.
Please note that historical total dam volume data changed when we added Stirling and Samson Brook dams.
We need steady regular rain to soak our catchments and get water flowing into our dams. Declining rainfall in Perth means that our dams receive much less streamflow than they used to. Streamflow is the amount of water entering our dams from our catchments and is measured by changing water storage levels.
The water in our dams is also no longer just made up of inflows from rain. Groundwater and desalinated water are also stored in our dams during periods of low demand, making it available in our warmer months, when it's most needed.
A number of regional dams levels are recorded manually by our teams every 2-3 days. Please note that sometimes circumstances prevent levels from being read, so there may be periods when data is unavailable.
Aside from the daily rainfall figures we display, you can also view monthly rainfall totals for Perth, including a graph showing a monthly rainfall comparison.
You can view the monthly rainfall, year to date and seasonal rainfall for the past 4 years in a chart or table view.
Rainfall data has been supplied by the Bureau of Meteorology since 1994.
We started recording rainfall data at all our dams in 1876, giving us our own historical records for this period.