NICK TURNER lives in White Gum Valley and is senior principal engineer at the Water Corporation. In this week’s THINKING ALLOWED he argues that if recycled drinking water is good enough for Disneyland in California, it’s good enough for fair dinkum Aussies back home.
I CAN completely understand why at first ‘flush’ readers might think of the yuck factor at the thought of drinking recycled wastewater (“Poo to People”, Herald letters, August 26, 2017).
I have been a passionate advocate of water recycling for years, and pioneered looking at groundwater replenishment with the Water Corporation for our local water supply.
My experience of over fifteen years interacting with people on the concept is that once the process is explained and people know how it works, fears are quickly allayed.
Based on a similar scheme in Orange County, California, groundwater replenishment involves taking treated wastewater at our treatment plant in Craigie and further treating it to strict drinking water standards, then recharging it into existing groundwater supplies.
The water then mixes with existing groundwater and is stored for many years in the natural groundwater environment before being extracted for further treatment, ready to be used for drinking water.
The treatment process includes putting the water through a filter so fine it removes any dissolved material larger than 1/300th of the width of a single human hair.
Any dissolved particles that are left are then removed through a process of reverse osmosis, where the water is put through tiny tubes 100th the size again of the pores used in ultra-filtration.
This is the same process that is used to remove the salt from seawater and transform it to drinking water.
At this point the water should be safe, but a final “insurance step” involves ultraviolet light disinfection to eradicate any micro-organisms that may still be left behind.
Once recharged into the groundwater system, it undergoes a natural filtration process through the soils of the aquifers the same as any rainwater or stormwater that soaks into the ground.
If you have ever visited Disneyland in California, chances are you have already tasted recycled water as this scheme has been used there since the 1970’s.
The Water Corporation trialled the approach for three years to demonstrate it was safe, ending in 2012.
More than 3.8 billion litres of highly treated recycled water was recharged into our groundwater supplies.
This gave us the opportunity to test the approach in local conditions and report to our regulators that the process was indeed safe.
Every one of the 62,300 water quality samples taken met strict health and safety requirements set by the department of health, including the Australian drinking water quality guidelines.
So why are we going to recycle wastewater? The answer is simple.
Since the 1970’s, rainfall has reduced in the south west of Australia by around 19 per cent, and the bureau of meteorology predicts this will continue to decrease.
Over the same period we’ve seen a decrease in streamflow into Perth’s dams and groundwater resources, from a post-1975 average of 189b litres per year to an average of 50b litres over the past five years.
In 2015 we hit a new low when the amount of streamflow was less than the annual evaporation from our dams.
Quite simply, we can no longer rely on rainfall in our dam catchments to supply our drinking water.
We are progressing with expansion of the groundwater replenishment scheme and within three years this will contribute about 10 per cent of the total water supply for Perth.
In the longer term groundwater replenishment could contribute up to 20 per cent.
Around a decade ago we started planning for the drying climate to build a more resilient water supply scheme for Perth that no longer relied on dams.
Part of this plan is a goal to increase water recycling to 30 per cent by 2030 and importantly, work with the community to reduce our water use by 15 per cent.
To find out more about the groundwater replenishment scheme, you can take a free tour of the visitor centre in Craigie and have all of your questions answered.
To book a tour, or read more about this recycling scheme, go to http://www.watercorporation.com.au/gwr