Goal 1
Providing clean, safe drinking water


Desalination

Rainfall in the Sydney catchment area is extremely variable. It is for this reason that dam storages were designed to hold up to eight years of water supply. In London and Tokyo, the storages are 12 weeks or less.

Rainfall in the catchment area also appears to be lower than in the past. It is too early to say definitely whether this is due to climate change, long rainfall cycles or some other factor.

The chart below is an estimate of the storage inflow into Warragamba Dam and the metropolitan dams over the last century. It excludes Shoalhaven transfers. The inflows reflect a 50-year cycle of low rainfall (to about 1950), about 40 years of higher rainfall to 1990, and what now may be a further low rainfall cycle.

The latest low rainfall period has yielded significantly less inflows than the higher rainfall period. Of more concern is that the recent low rainfall period has much lower inflows than those of the earlier part of the last century.


Inflows to Sydney's Hawkesbury-Nepean dams (excluding Shoalhaven transfers)

Desalination-graph Annual inflows to Sydney's dams (billion litres) 1909 to 2006
Source: Sydney Catchment Authority

Dam storages and inflows

Sydney, the Illawarra and the Blue Mountains also have an increasing population. Since 1974, the population has increased by over a million. In the next 25 years, the population will increase by another million.

The highly variable and uncertain rainfall and the city's growing population mean that more water is needed to guarantee Sydney's water supply.

In February 2007, Sydney Water released requests for tenders for a desalination plant. Dam storage levels were at 34 per cent. At this level, there is about three years of water storage, and to construct a desalination plant takes about two and a half years. Leaving the decision longer would have led to a risk of running out of water.

Powered by renewable energy, the desalination plant will produce up to 250 million litres of water a day. This is about 15 per cent of the water supply. If necessary, its capacity can be increased to 500 million litres a day. This source of water does not depend on rain and adds significantly to the security of the water supply.

Drinking water produced by the plant will be treated to standards that meet Australian Drinking Water Guidelines and NSW Health requirements. It will be indistinguishable from Sydney's current drinking water.

The desalination plant will use reverse osmosis technology. Seawater is drawn into the plant through a membrane at high pressure. The membrane acts like a microscopic strainer that removes salt and other impurities from seawater to produce drinking water.

Around 60 per cent of the water drawn into the plant will be returned to the ocean as seawater concentrate. The concentrate will be mixed back into the ocean. It is within natural seawater salinity around 50 to 75 metres from the discharge point.

The discharged seawater concentrate is one to two degrees warmer than the water drawn into the plant. The ocean goes back to normal within 75 metres from where the discharge is released into the Tasman Sea.

Sydney Water will ensure that the marine environment is protected during the construction and operation of the desalination plant. Sydney Water has already started a marine and estuarine monitoring program to monitor ocean and bay water quality and ecology.

The following measures will prevent impacts on local flora and fauna:

  • maintaining or replacing habitat for animals
  • constructing the pipeline in areas with very little vegetation
  • avoiding damage to large native trees
  • controlling noxious and exotic weeds
  • replanting native plants in areas that trenching has disturbed
  • removing construction debris and soil as soon as possible.

The desalination pipeline route in the bay is over bare sand or patchy seagrasses. The small sections of seagrasses will be replanted or avoided.

Community impacts along the desalination pipeline route will be minimised as much as possible. 'Trenchless' construction methods, such as micro tunnelling, will be used where possible instead of digging up streets. Once construction is finished, streets and all work areas will be restored in consultation with the community.

The desalination plant will be owned by Sydney Desalination Plant Pty Ltd. This is a wholly owned subsidiary company of Sydney Water. The subsidiary company has been established to ensure transparency and accountability for the delivery and operation of the desalination plant.

The plant is scheduled for completion in 2009-10. The contract for the plant's construction and operations is on the Sydney Water website.

Desal proposed site Proposed desalination site


Desal Plant layout How the desalination plant works