From rainfall to reservior: The journey of your water
21 October 2026
Have you ever thought about the journey water has to take from rainfall to reach water storage?
What people may not realise is that rain may have fallen many kilometres away in one of Melbourne's protected catchments before arriving at a reservoir, and well before reaching a drinking water tap in Greater Western Water's vast service area.
GWW’s General Manager Strategy and Partnerships Kessia Thomson said it was a journey worth thinking about during National Water Week and especially as we head into dry conditions and summer.
“The time it takes can depend on the intensity of the rain, and the dryness of the ground that it falls on. If it rains directly over a reservoir, storage levels can increase quickly or in a couple of hours. Most rain never makes it to storage, with a significant amount evaporating or getting used by plants and soil if it’s dry.
“Sometimes, rain falling across the catchment can take days, weeks or months to reach storages, depending on where the water travels through the landscape and other factors. This also means that a reservoir can rise even when it’s not raining.”
For most GWW customers, rainfall reaches storages through a network of protected catchments, rivers, reservoirs and creeks in the Yarra Ranges and surrounds.
From there it runs into some of Victoria’s largest reservoirs before being transferred through Melbourne Water’s network to customers, including those serviced by GWW.
In the northwest of GWW’s service area, rainfall follows a different pathway via local catchments and waterways and into reservoirs such as Rosslynne, Merrimu and Pykes Creek. It also finds its way to smaller storages in the Macedon Ranges.
In addition, alongside a mix of water sources, some regional towns use groundwater aquifers and local bores to help with water supply during times of low rainfall.
Meaningful water storage recovery for the large reservoirs often required weeks or months of rainfall, not just a single rainfall event, Kessia said.
“One big storm isn’t always enough, and that’s part of the reason why using water wisely is important at all times. As our climate becomes hotter and drier, we can no longer depend on rainfall alone to fill our water storages.
“To illustrate this need, consider that to help bolster Melbourne’s water supplies, 150 billion litres of water was ordered from the Victorian Desalination Plant for the 2026/27 supply year and is already being delivered to keep our taps flowing.
“We can all help to make a difference. Small water-saving actions at home add up across our community and help protect our precious water supplies.
“Simple changes like shorter showers, fixing leaky taps and smart garden watering can make a real difference.”
