Water storage reservoirs

Get to know Melbourne’s water storage reservoirs, which help secure our water supply now and into the future.

What is a reservoir?

Aerial shot of Tarago Reservoir
Aerial view of Tarago Reservoir

A reservoir is a large natural or artificial storage of water often formed by constructing a dam across a river.

Our 10 major reservoirs store water collected from the catchments, as well as water supplied from the Victorian Desalination Plant. Together, they have a storage capacity of 1,810 billion litres, and vary in size from the smaller O’Shannassy Reservoir (3 billion litres) to the massive Thomson Reservoir (1,068 billion litres).

 

Looking for daily water storage levels? Find them at our most visited page, Water storage levels.

Types of reservoirs

There are two types of reservoirs

  • on-stream reservoirs, where rainfall across Melbourne's water catchments drive the amount of water that flows into these reservoirs.

  • off-stream reservoirs, where water is transferred from on-stream reservoirs or other sources: for example, Sugarloaf Reservoir, which can receive water from the North-South Pipeline.

The reservoirs are connected so we can move water around the water supply system, based on factors such as rainfall and demand.

Did you know: Thomson Reservoir is the largest, but most of Melbourne’s water is supplied via Silvan Reservoir. Read why

On-stream reservoirs

Meet our on-stream reservoirs, their capacity and how they are fed. Click to discover what makes them unique:

Reservoir​ Source of water​

Capacity (billion litres)​

Thomson​ ​Thomson catchment, located in Thomson State Forest and a small part of Baw Baw National Park ​1,068
Upper Yarra​ ​Upper Yarra catchment, in the Yarra Ranges National Park ​200
Tarago​ ​Bunyip State Forest 37​
Yan Yean ​Combination of Toorourrong catchment, Silvan Reservoir and Winneke treatment plant ​30
Maroondah ​Watts River catchment and Graceburn Creek ​22
O'Shannassy ​O’Shannassy River and Smith Creek ​3

Off-stream reservoirs

Meet our off-stream reservoirs, their capacity, and the areas they supply water to. Click through for more details.

Reservoir​ Areas supplied​ Capacity (billion litres)​
Cardinia​ ​Most parts of Melbourne, especially the south and south-eastern suburbs ​287
Sugarloaf ​North, west and central Melbourne ​96
Silvan​ ​Most parts of Melbourne ​40
Greenvale​ ​North-west and west Melbourne ​27

 

The water supply system

 

We have a complex water supply system, where some of our reservoirs are connected, allowing us to move water between reservoirs when we need to. For example, we might move water out of a reservoir so it can fill up  during a heavy rain event or move water to meet the demand  in different areas.

We operate, maintain and upgrade our water supply system to ensure we have the right water supply for Melburnians and the surrounding region now and for the future. Managing the water supply system is a dynamic situation, satisfying water demands that vary hourly while dealing with seasonal and annual changes in water availability, from sometimes long, dry seasons periods to wetter years. That’s why desalinated water plays a critical role in securing our water supply by building an important buffer in our storages each year, that can take the pressure off our water supply during drier periods and droughts. Retaining a higher volume of water in reservoirs is important as we know that drought can creep up on us quickly.

How we calculate water storage levels

Long shot of dam

Melbourne’s water storage levels are expressed as a percentage of the combined capacity of all storage reservoirs.

This is more accurate than looking at individual reservoirs because of their vast differences in storage capacity. For example, the amount of water needed to completely fill O’Shannassy Reservoir would only fill 0.3% of Thomson Reservoir.

Did you know that without that extra water supplied by the Victorian Desalination Plant, our storages would be around 19% lower?

See how we calculate data

Last updated:
9 September 2021