Discovering groundwater replenishment (video transcript)

This is a transcript for our video that explains how groundwater replenishment works, and why it is important.

Oscar (voice-over): Water Corporation is the main 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 (to camera in the laundry at home): You might already know that the water you use in your home goes to a wastewater treatment plant. There, it’s treated to make it safe enough to return to the environment. You may even know that this treated wastewater can be recycled to water parks and ovals, or be used by industry. But, did you know there is something else we can do with treated wastewater that will help provide drinking water for future generations? It’s called groundwater replenishment.

Oscar (to camera outside the recycling plant in Craigie, WA): This advanced water recycling plant in Craigie is where it all started in Perth. It’s where Water Corporation did a three-year trial to make sure groundwater replenishment could be done safely, effectively and with community support. The trials’ success has paved the way for groundwater replenishment to be done on a much larger scale.

[Walk through front gates] 

Siobhan: Hi Oscar welcome to the plant.

Oscar: Hi Siobhan.

Siobhan: Let’s find you some PPE gear and we can look inside.

Oscar: Sure. [Oscar appears in Personal Protective Equipment (PPE)] 
So Siobhan, what exactly is groundwater replenishment? 

Siobhan: Groundwater replenishment is where we take treated wastewater, put it through further treatment so that it meets drinking water standards, and then put it deep into the ground. Years later, it can be taken out, treated again and added to our drinking water supply. So it’s basically recycling water, using aquifers to store and naturally filter the water until we need it.

Oscar: But we’re not drinking it yet, are we?

Siobhan: No. Think of it like a savings account – we’re putting it in the bank for the future.

Oscar: I’m not sure I like the idea of drinking treated wastewater – sounds a bit yuck.

Siobhan: Some people do feel that way, and that’s part of the reason why we have done  the trial – to let the community know how it works and address any concerns. Hopefully after today, along with thousands of other people who’ve toured the plant, you’ll feel differently. 

[Oscar looks to camera with uncertainty]

Siobhan: Okay, let’s go.

Oscar (voice-over)[Footage shows a water fall]
Before we take a look at the plant, it’s important to understand a bit about our groundwater system. When it rains, our dams, lakes and rivers fill up, and water trickles down through rocks and soils into 'aquifers'. Our aquifers aren’t the underground rivers and lakes you might imagine – they’re actually made up of materials such as sand, sandstone and limestone, and water moves between the particles. We’re lucky in Perth because we have a vast groundwater system that provides around 40% of our drinking water. But our decreasing rainfall means less water is going into our rivers, dams and, in some areas, groundwater. That’s why we need water sources that don’t rely on rainfall. 

[Return to the recycling plant]
Oscar: So, what have we got here Siobhan?

Siobhan: This is the intake pipe where treated wastewater from the Beenyup Wastewater Treatment Plant over there [pointing] comes in.

Oscar: So this water has already been treated to remove chemicals and microscopic organisms?

Siobhan: Yes, and every day we can take millions of litres of it and, by putting it through this plant, turn it into water that is drinking water quality.

Oscar: Sounds pretty impressive.  How does it all work? 

Siobhan: We store the incoming treated wastewater in this tank, to  manage the flow. Once it’s here, it goes through 3 stages – ultrafiltration, reverse osmosis and ultra violet disinfection.

Oscar:  Whoa, that’s way too technical for me.

Siobhan: Sorry Oscar! Why don't we go inside and I can explain it a bit better.

[Inside the recycling plant]
Siobhan: This first section holds the ultrafiltration units.  Each vertical unit looks like this inside. [Show full tube sample and then cross-section] This cross-section gives you a better idea.

Oscar: Looks a bit like spaghetti to me.

Siobhan: Those are the ‘filtration tubes’.There are about 7000 in each cylinder.

Oscar:  But if they’re like spaghetti, how does the water get through?

Siobhan: They’re actually more like tubular pasta or like a straw.  And, although we can’t see them, each one has tiny holes that are about 1/300th the width of a human hair! The water is pushed through the tubes, taking out the larger molecules.

[Oscar holds up a strand of hair from his fringe]

Oscar: Just out of interest, how long would it stretch if you joined all the straws?

Siobhan: It would stretch from Perth to Darwin — about 2,700 kilometres.

Oscar: Wow, that’s a lot.

Siobhan: So these are the ultra filtration cylinders and the spaghetti bit that we were looking at earlier, those are all inside here.

Oscar: Gosh they are so tall and so many of them.

Siobhan: A lot of water goes through.  

Siobhan: Next is reverse osmosis.

Oscar: I thought that was used for seawater desalination?

Siobhan: It is, but we also use the same technology here. High-powered pumps push the water under very high pressure through the membranes.

Oscar: Are these similar to the ultrafiltration membranes?

Siobhan: They’re a bit different. Instead of tubular pasta, they're more like large lasagne sheets tightly wound and with microscopic holes that are 100 times smaller than those in the ultrafiltration units. 

[Show reverse osmosis membrane sample.]

Oscar: That’s a pretty small hole. So I’m guessing anything that isn’t a water molecule is going to have a pretty tough time getting through that?

Siobhan: That’s exactly right. And it takes a lot of pressure. In fact, the pressure in the reverse osmosis units is around 1000 kilopascals — which is the same about of pressure  it would take to push  one litre of water 1000 metres up into the air!

Oscar: Wow, that’s like a 200 storey building!

Siobhan: Yes it is.

Siobhan (voice-over): The last stage is ultra-violet disinfection. The ultra violet, or UV, light acts as a final safeguard, zapping and destroying any micro-organisms that might be left. Once the water has been through all 3 stages, it is ready to go into the ground.

Siobhan: This is the recharge bore where the water is pumped into the aquifer. 

Siobhan (voice-over): The pipe goes down 220 metres and the bottom half has small holes that evenly distribute the water. Once it’s in the aquifer, the recycled water is filtered naturally. But even before it goes into the aquifer, remember that this water is clean. 

Oscar: Okay, you’ve talked me into it. Let’s have a taste.

[Presents an empty glass]

Siobhan: Uh, we’re not actually allowed to drink it yet.

Oscar: Why not?

Siobhan: Well, for one, there are regulations and guidelines that we need to follow. When we did the trial, it was to put the recycled water into the ground, not to be used as drinking water. Another reason is that this recycled water is almost too pure to drink, like distilled or purified water. To make it suitable for drinking, we need to add minerals and fluoride.

Oscar: And that happens way down the track doesn’t it, when we want to take it out of ‘the bank’?

Siobhan: Yes, you’re getting the hang of it.

Oscar: Okay, the water is in the ground. Now what happens? 

Siobhan: Mostly, we just let nature take its course. But we do continue to monitor and test the recycled water. These boxes are the monitoring bores where we can take water samples and send them to labs for testing. They also help us to determine how fast and in what direction the water is travelling.

Oscar: So how fast does the water travel?

Siobhan: It actually moves pretty slowly in the ground. During the 3-year trial, it  moved  about 200 metres. As we continue to  put more water in the ground, it might move more quickly, but it will still take years, even decades, for  it to reach a bore where we can take it out and add it to the  drinking water. 

Oscar: How do you tell the difference between existing groundwater and the recycled water?

Siobhan: Good question. It’s actually by temperature and by level of salinity. But over time, the existing  water will mix with the recycled water and become pretty much  indistinguishable.

Oscar: You mean you won’t be able to tell the difference?

Siobhan: Exactly.

Oscar: This all sounds impressive, but how do you absolutely make sure the recycled water is safe?

Siobhan: Well, we have checkpoints throughout the plant. They measure different aspects of water quality. If the water doesn’t meet the standard for a particular check point, it triggers an alert for us to take action and that may mean diverting the water.

Oscar: So, the trial has been done, groundwater replenishment is approved and the community support the idea. What’s next?

Siobhan: Water Corporation is building Australia’s first full-scale groundwater replenishment scheme. It will be like this one, just much bigger.

Oscar: How much bigger are we talking?

Siobhan: One of the new recharge bores will go down 754 metres into the Yarragadee aquifer. In terms of capacity, the new plant will initially be able to produce 14 billion litres of recycled water each year, and eventually be able to produce 28 billion litres each year. That's enough to supply up to 100,000 Perth households for one year.

Oscar: Wow!

Oscar: Okay, you’ve convinced me. I’m over the yuck factor. I’m confident it’s safe and all under control. And I know how important it is to have another water source that doesn’t rely on rainfall.

Siobhan: Great. My work here is done.

[Both turn to walk away; music plays]