Treating groundwater for drinking (video transcript)

This is a transcript for our video that looks behind-the-scenes at our Groundwater Treatment Plant in Wanneroo.

Oscar (voice-over): Water Corporation is the main provider supplier of water, wastewater and drainage services in Western Australia. It helps to ensure we have enough drinking water for the future by developing new sources, increasing water recycling and encouraging efficient water use.

Oscar: We know that the water we use in our homes, schools and businesses is clean and safe for us to drink. But do you ever think about where that water comes from, and the journey it takes to arrive at your home?

Oscar (voice over): In Perth, we have four main sources of drinking water – surface water, groundwater, seawater and groundwater replenishment. Surface water is the rainfall that flows into our dams.  This has given us a reliable water source in the past, but our drying climate means there is less rainfall and, as a result less water in our dams. We also have a vast groundwater system that provides about 40% of our drinking water, and this is also a never-ending source and it also relies on rainfall to top it up. Seawater is a resource that doesn’t rely on the climate, and now seawater desalination plants make a sizeable contribution to our drinking water supply

Groundwater replenishment is the newest water source, which involves treating wastewater to drinking water standards and recharging it into existing groundwater supplies.  The water is then stored and removed some time later for further treatment, ready to supply our drinking water system.

Oscar (to camera): Like all water that makes its way into our drinking water system, groundwater needs to go through a thorough treatment process to make it safe for us to drink. Today, we’re going to find out about how that’s done, here at the Wanneroo Groundwater Treatment Plant.

Siobhan: Hi Oscar, how are you going?

Oscar: Hi Siobhan, I'm good thanks. So Siobhan, how is water treated to make it drinkable?

Siobhan (voice over): There are different processes for treating water, depending on where it comes from and the quality of the water to begin with. Here, we take water from groundwater bores and we put it through five basic processes — aeration, MIEX, clarification, filtration and disinfection. Generally most of the plants across Western Australia use standard treatment. However at this plant we treat the water using MIEX, a special, innovative pre-treatment process which stands for Magnetic Ion Exchange. It helps treat the variable water quality of Perth’s groundwaters. I’ll explain this in more detail later

Oscar: So where is the water at this plant coming from?

Siobhan: It comes from bores at two main locations north of Perth — Wanneroo and Pinjar. Bores are basically vertical pipes that go down into aquifers. Aquifers are an area underground where water is stored between rock formations.

Oscar: Are these the same as garden bores we have at home?

Siobhan: They’re similar, but they operate on a much larger scale. Your average garden bores can source water underground at depths around 50 to 100m. The bores for Wanneroo can go down up to 800 meters, where the water is relatively warm (37ºC). Here you can feel how warm the water is.

Oscar: Whoa.

Siobahn: Yes that is 37 degrees.

Oscar: Okay, so you’ve taken the water out of the ground. What’s the first step in the process?

Siobhan: The water that comes in from the bores has high levels  of organic material , like iron and hydrogen sulphide and that’s what gives the water its brown colour. When the groundwater comes into the plant, the first process is called aeration and as you can see, air is being blown into the water and this increases the oxygen levels.

Oscar: Why is that important?

Siobhan: The oxygen helps to separate out the iron and hydrogen sulphide both of which occur naturally in the groundwater. Iron gives the water that rust colour — and you can sometimes see this on fences that have been exposed to groundwater from garden bores.The hydrogen sulphide is a gas has a really strong smell, it’s a bit like rotten eggs.

Oscar: Eurgh, I’ve definitely smelt that coming from garden bores! 

Siobhan (voice-over): The Wanneroo Groundwater Treatment Process uses an innovative water treatment process – MIEX after aeration. At full capacity of the plant, half of the water is treated by MIEX, while the other half is treated by the standard treatment process. Chlorine is added to the water before it enters the MIEX or standard treatment processes, to help separate any iron that was not removed fully through the aeration process.

Oscar: What exactly is MIEX and why don’t you just stick with the standard treatment?

Siobhan: Well like I said before, MIEX stands for Magnetic Ion Exchange. While the standard processes do remove some of the organic material from  the water, MIEX process is more efficient in removing a wider range of this material. So it  means we can consistently and more efficiently treat the water.

Siobhan (voice over): Once the water has been treated by MIEX, it comes into these large tanks which are called clarifiers. At the clarifiers, a chemical called ‘alum’  is used to help separate the colour and turbidity particles in the water. These particles bind to alum and become heavier than the water. 

Siobhan (to Oscar): We also add Poly electrolyte which is a primary flocculant chemical which helps the particles to separate from the clean water by allowing them to sink to the bottom of the tank. 

Oscar: What exactly is the difference between the MIEX and standard treated water at this point?

Siobhan: Well we need to get the chemistry of the water right, and pH is an important part of controlling the treatment process. Now the water that has been treated by MIEX doesn’t need any pH adjustment. However the water that has been treated by the standard process does, and to do that we use lime.

Siobhan: After clarification, the water from both the MIEX and standard treatment processes come together for filtration. 

Siobhan (voice over): Here, the water goes through deep bed filters, which contain carbon, sand, and blue metal to remove any particles that may have carried over from the clarifiers. The filters are regularly cleaned by backwashing — which means that the water goes in the reverse direction to push out particles in the filter. The backwash water goes back to aeration the first step in the process to be treated again. 

Oscar: And what happens to the particles that have been cleaned out of the filters?

Siobhan: We call that ‘sediment’, and it goes to drying beds and then goes to landfill sites.

Siobhan: After filtration, the water goes into the clearwater tank, which is the last step before its added to our drinking water supply. Before it goes into these tanks however, we’ve added fluoride and chlorine to make it suitable for drinking.

Oscar: So, after the water has been through the full treatment process, where does it go?

Siobhan: We move it to the Wanneroo Reservoir and then it feeds into a network of pipes that supply the northern suburbs of Perth.

Oscar: Throughout this process, how do you make sure the water is being treated properly?

Siobhan: We have checkpoints along the way, that measure different aspects of water quality. This is all captured by our monitoring and control system that allows us to keep track of it. We also ensure water quality by testing all the water supply sources in Western Australia. 

Oscar: Thanks Siobhan. Now that I’ve seen all the work that goes into making water ready to drink, I have a whole new perspective on the water that comes out of my tap.

Siobhan: Well that’s great its really a precious resource and we should always be mindful of how much we use. So thank you very much for coming.

Oscar: Thank you very much for having me.