Groundwater Replenishment FAQs

What is reverse osmosis?

Reverse osmosis is a process where a membrane with very tiny holes acts like a microscopic sieve to strain contaminants out of water. Reverse osmosis membranes allow water molecules to pass through, but not larger compounds. As water is a very small molecule, almost everything else, including viruses, pathogens and most chemicals can be removed, leaving very pure water.

Reverse osmosis is currently used to desalinate seawater at Perth’s new desalination plant.

It is also used to treat wastewater from the Woodman Point Wastewater Treatment Plant for use by industry at the Water Corporation’s Kwinana Water Reclamation Plant.

What is wastewater?

Wastewater is household water, including water from the bathroom, kitchen, laundry and toilet. It also consists of some water from industry.

Wastewater can be treated to many different standards so it can be recycled or safely discharged to water bodies, such as rivers or oceans.

Why can’t we use recycled water for other purposes, rather than drinking it?

Recycled water  is already used for a range of purposes including the irrigation of parks and gardens, recycling greywater from the home, irrigating agricultural produce and supplying recycled water for industrial use. Many different options have been explored and implemented including:

Groundwater replenishment is just one of a series of opportunities to make better use of recycled water. Some of the benefits of groundwater replenishment include:

• it can help to maintain groundwater levels in low rainfall periods, making it an environmentally sustainable water source;
• it uses naturally occurring groundwater aquifers to store and use water as required;
• it makes use of existing water supply infrastructure;
• it allows us to recycle large quantities of water
• it makes us less dependent on rainfall in a drying climate; and
• it is relatively cost effective, costing around the same as  seawater desalination.

Will groundwater replenishment affect our drinking water quality?

Currently, Perth’s drinking water comes from dams and groundwater supplies. In fact, around 60% of our drinking water comes from groundwater.

The reverse osmosis treatment process is so effective it actually removes essential minerals and salts. To address this, certain types of natural minerals would be added back to the water before it is injected into the groundwater to ensure it mixes effectively.

To demonstrate that the technology is safe, the Water Corporation is conducting a three year groundwater replenishment trial and also participating in a series of research projects with universities and research organisations such as the CSIRO.

What will groundwater replenishment cost?

Early estimates indicate that the cost of implementing a full groundwater replenishment scheme (25 gigalitres per year) is between $1 and $2 per kilolitre.  This is comparable to other new water sources, such as seawater desalination.

Are there any risks associated with groundwater replenishment?

Potential risks include:

While national and international research has demonstrated that the risk to the environment or to people is relatively low, there are a series of research projects that the Water Corporation, in conjunction with scientific agencies, universities and other government bodies is undertaking before a full groundwater replenishment scheme will be considered.  

Project partners include the CSIRO, Curtin University of Technology, the Chemistry Centre, the University of Western Australia and the Departments of Water, Health and Environment and Conservation.

Some communities have actually been drinking recycled water for several decades. Indirect or "unplanned" drinking water recycling occurs where treated wastewater is discharged into a water source (ususally a river) and then becomes part of a drinking water supply for a community downstream. This practice occurs in the Murray River, Australia which supplies many towns and cities with drinking water.

Is groundwater replenishment carried out anywhere else?

Yes. Groundwater replenishment is used in Orange County, California and Scottsdale, Arizona to supplement drinking water supplies.

From December 2008, South East Queensland's drinking water supplies will be supplemented with purified recycled water.  Drinking-quality recycled water will be blended into Wivenhoe Dam.  For more information visit www.qwc.qld.gov.au/Purified+Recycled+Water

Reverse osmosis technology is also used in Singapore where 1% of recycled water is added to a major drinking water dam, rather than groundwater.

Why will groundwater replenishment take so long to get under way?

The Water Corporation will need to obtain environmental and health approvals before groundwater replenishment can become a viable water supply option. Part of the approvals process is to run the three year trial to demonstrate that the risks to the environment and human health are negligible.

It will also take some time to build the reverse osmosis plant required for the trial and for the full groundwater replenishment scheme.