Our Water Matters: Desalination Down Under

Perth is a coastal city of 2 million people in Western Australia (WA) that has experienced major climate impacts in recent decades. Rachel Miller, head of water quality at WA’s Water Corporation, stated in a recent radio interview that the water mix has seen a “heavy impact in Perth” due to climate change and steep reductions in rainfall. “We used to see a lot more streamflow runoff from our catchments [reservoirs] years ago and we used to see surface water contribute a large proportion of our water supply. Now, we’re seeing surface water contribute at most 20%.” The drying climate has forced WA’s Water Corporation “to produce other different kinds of water sources to keep our city replenished and help it to grow.” Perth’s current potable water mix includes 30-40% groundwater and 10-20% recycled water with the remaining portion covered by desalination.  “We’ve worked hard here in the Water Corporation to build a water supply mix which means that when we have good years, we can use our high-quality sources and when we have poor years, we can use manufactured water to supply Perth. That way the water is 100% safe. But also, the city can grow.” 

With its motto of “fresh water thinking,” WA’s Water Corporation is no stranger to innovation. According to Miller, it is “one of the first utilities in the world, along with Singapore and Orange County in California, to do groundwater replenishment, which is treating wastewater for drinking water.” It also built the first desalination plant in Australia in 2016. “So, we’ve had a lot of innovation, a lot of world experts based in Perth to build in this resilience and security with the different water sources.” 

The strategy relies heavily on desalination, the process of converting seawater to potable water. In its film titled “What happens at a Seawater Desalination Plant,” WA’s Water Corporation explains that desalination involves “five main stages: seawater intake, screening, ultrafiltration, reverse osmosis and finally, water treatment.” The seawater enters the system via intake towers located about 500 yards from shore in the Indian Ocean where the water is about 40 feet deep. The seawater flows into these towers via gravity at a very slow rate, which enables fish and other marine life to easily swim away. This intake flow passes through screens to remove seaweed and other ocean debris. The seawater is then pumped through a series of ultrafiltration filters to remove viruses and bacteria. 

This ultrafiltered water subsequently undergoes reverse osmosis (RO), a process involving a complex system of membranes. The water is forced through these membranes at 57 bar, which is enough pressure to push a column of water more than 570 yards vertically up into the air. It is the generation of this pressure that makes seawater desalination four times more energy-intensive than groundwater collection and over 40 times more energy-intensive than water sourced from reservoirs. But Water Corporation’s RO systems employ sophisticated energy recovery devices (ERDs) that reuse the pressure energy of the process, which greatly reduces the pumping necessary to pressurize the flow of the ultra filtered seawater.

According to Energy Recovery, a California-based company that manufactures these devices, ERDs “are at the core of saving energy in the operation of any seawater reverse osmosis (SWRO) desalination facility. Isobaric or ‘positive displacement’ devices … are the most efficient solution available today and can reduce the energy consumption of SWRO systems by up to 60 percent.” In addition to these built-in efficiencies, Water Corporation has also partnered with regional power suppliers to construct large-scale wind and solar farms in Western Australia to offset its energy use.

Once the water has completed the reverse osmosis process, it is further treated with minerals and disinfected to make it safe for drinking. The plant’s daily output equals the volume of about 122 Olympic-sized swimming pools. This volume is added to the water supply or stored in reservoirs for future use. About half of the seawater that enters the plant becomes fresh drinking water. The other half of the seawater as well as the salt and impurities removed from the processed seawater are returned to the ocean via diffusers. The design and location of these diffusers ensure that the discharged concentrated seawater mixes quickly to minimize any effects on sensitive marine habitats.

Water Corporation’s resilient mix of resources provide Perth and Western Australia with the flexibility necessary to better manage the challenges of a hotter, drier future. 

Visit watercorporation.com.au/our-water to learn more. 

Trey Gerfers is a San Antonio native and serves as general manager of the Presidio County Underground Water Conservation District. He is also chairman of the Presidio County Water Infrastructure Steering Committee and president of the Marfa Parks and Recreation Board. Trey has lived in Marfa since 2013.