Teacher background information
Water recycling is a general term for the reclamation, treatment and reuse of water for new purposes. Recycled water can refer to water sourced from wastewater, greywater, groundwater, stormwater and rainwater for a variety of purposes, such as:
- drinking water;
- irrigation of recreation grounds;
- groundwater replenishment;
- irrigation of non-food crops;
- household toilets; and
Regardless of the source, water to be recycled must be fit-for-purpose, which means that it must be treated to an appropriate level for its intended final use.
For the purpose of this booklet, the recycled water we refer to will be from wastewater sources.
Water recycling is essential to maintaining a reliable, sustainable and safe water supply for Western Australia and is a key part of Water Corporation’s climate resilience strategy. Increasing the amount of water that is recycled is crucial to managing our precious drinking water resources efficiently and making the most of our wastewater resource that is often ‘wasted water’.
Groundwater replenishment is the process by which secondary treated wastewater undergoes further advanced treatment to produce water which is safe to drink and meets Australian guidelines for drinking water. At this point it is then recharged into an aquifer for later use as a drinking water source.
Groundwater Replenishment Trial (GWRT)
Water Corporation ran a three year trial of groundwater replenishment from 2010-12. It consisted of operating the Advanced Water Recycling Plant (AWRP) located on the same site as the Beenyup Wastewater Treatment Plant (WWTP), in Craigie, and then recharging the recycled water into the Leederville Aquifer on the site.
During the trial plant’s operation 85,644 water quality samples were taken. This included samples taken throughout the treatment process, at the point of recharge and groundwater samples. All of these samples consistently met stringent health and environmental guidelines. In addition to this, it was vital that we gained community support of groundwater replenishment in order for the trial to be a success and various community engagement initiatives were developed to gain community acceptance (see fact sheet ‘The value of community acceptance for groundwater replenishment’ for further details).
The success of the trial has meant Water Corporation is now embarking on the development of Australia’s first full-scale groundwater replenishment scheme.
Groundwater replenishment process
Before wastewater reaches the AWRP, it undergoes biological treatment at the Beenyup WWTP to make the water suitable for both discharge to ocean, and for further treatment for recycling purposes. The wastewater treatment process removes some chemicals and micro-organisms, such as bacteria. It also removes most nutrients, detergents, oils, pesticides and heavy metals.
Treated wastewater that reaches the AWRP undergoes further multiple treatment processes which include:
Step 1 – Ultra filtration
Step 2 – Reverse osmosis
Step 3 – Ultraviolet (UV) disinfection
These treatment measures remove chemicals and micro-organisms in accordance with Australian guidelines for drinking water. Throughout the treatment process, water is continually monitored to ensure water quality is met.
At the end of the AWRP treatment process, water is recharged into groundwater 120 to 220 metres underground, into the confined Leederville aquifer and 754 metres into the Yarragadee Aquifer.
The Groundwater Replenishment Scheme
Stage 1 of Australia’s first full-scale groundwater replenishment scheme is planned to have the capacity to recharge 14 billion litres of recycled water annually. Subsequent stages will see the scheme ultimately deliver around 28 billion litres per year. By 2060, it is possible groundwater replenishment could contribute up to 115 billion litres each year by recycling water from Perth’s major wastewater treatment plants. This could account for up to 20% of total annual drinking water supply.
Groundwater replenishment around the world
Perth’s groundwater replenishment technology was based on that of Orange County, California (USA). Orange County Water District has been using a similar approach since the 1970s. Other water recycling schemes that supplement drinking water supplies also exist in Singapore, Hampton (England) and in Windhoek (Namibia). Since 2003, Singapore has mixed approximately one percent of recycled water with dam water for drinking. However, in Perth, groundwater replenishment returns the recycled water to deep groundwater reserves for storage, rather than directly into a dam or water pipes used for public drinking water supplies. The groundwater is then abstracted some years later, treated as per standard groundwater treatment processes and added to the drinking water supply.
Approaches to potable reuse
Drinking water or potable water is water safe enough to be consumed by humans or used with low risk of immediate or long term harm. The recycling of water from wastewater for drinking can be referred to as either direct or indirect potable reuse. There is some debate regarding the interpretation of direct and indirect reuse, however we have summarised the definitions as defined by the Australian Department of Health and Aged Care.
Direct potable reuse can be defined as either the injection of recycled water directly into the potable water supply distribution system. Injection could be into a service reservoir or directly into a water pipeline and therefore the recycled water used by customers could be either slightly diluted or undiluted. There are no current examples of direct potable reuse in Australia. Internationally, the nearest example is in Singapore where they have branded their recycling program NEWater. NEWater is primarily for non-potable industrial uses but a small percentage of NEWater is mixed with raw water in the reservoir before treatment and then supplied to customers as tap water.
Indirect potable reuse can be defined as recycled water returning to the water cycle a significant distance upstream of the water treatment plant. This distribution could be into a major water supply reservoir, a water source which feeds a reservoir, or into a water supply aquifer. This recycled water would likely be greatly diluted with other ‘natural’ water before its next use.
Indirect reuse provides a separation between the treatment plant and the next user. This type of potable reuse is currently a more acceptable approach for the community as it depends to a lesser extent on the reliability of technology, and incorporates ‘natural’ processes within the reuse system to improve the perceived water quality.
For further information search:
Other organisations websites
The following organisations may also be able to provide resources:
- Groundwater replenishment system – purification steps
- PUB Singapore’s national water agency – NEWater
- Earth magazine – Drinking toilet water
- Department of Health and Aged Care – Review of health issues associated with potable reuse of wastewater
- Nabia water reuse