Perth’s shrinking Groundwater

Most of Perth’s water comes from the Gnangara groundwater mound (aquifer), stretching from north of Perth to the Swan River, as far south as Fremantle.

The Gnangara Mound is an important source of water for public water supply, irrigated agriculture, parks and gardens, industry and groundwater dependent ecosystems. Groundwater levels across the Gnangara Mound have generally been in decline for the last thirty years. This coincides with a general trend of declining annual rainfall across the south west of Western Australia. [1]

decreasing groundwater levels across the Gnangara Mound
This also coincides with the enormous amount of water we extract, particularly for horticulture and agriculture in Wanneroo and the Swan Valley and irrigation for public open space (parks, sporting ovals and golf courses, covered in grass as far as the eye can see). Groundwater irrigation for horticulture and agriculture south of Fremantle is also excessive, but this is from a different aquifer (which is probably declining just as much).

We waste vast amounts of water in Perth (and our government tries to make up for this wastage with desalination plants). There is no restriction on industry/ agriculture use and very little restriction on household use. Barely any grey water or processed black water (sewerage) is reused in any form. Run-off from roads ends up in storm water drains which empty into the sea (this would make a perfect source for irrigation). Huge expanses of suburbia are given over to lawn (residential gardens, parks, sporting fields and golf courses) which need (and receive) reticulation during our dry summers. Local parks, schools and golf courses often use bore water, but these bores are connected to the Gnangara Mound, contributing to its depletion. Water is sprayed on building sites to keep down dust which is a problem in our windy city.

Only in October 2007 were restrictions placed on summer bore use, for irrigating residential gardens, parks, sporting fields and golf courses. Theoretically restrictions shouldn’t be needed in winter months because you’d think people would realise that irrigation isn’t necessary when it’s raining. Sadly, I’ve seen sprinklers in use at Curtin University and gardens near my house, when it was raining.

I read an article in the magazine of the WA car club (RACWA) about saving water [2]. (If you’re looking for the article, it was in the June issue, not the most recent one.) I think the RAC realised that an organisation whose sole purpose is to promote car use needs a bit of greenwashing in these eco-conscious times. Every issue of their magazine has more and more environmental articles. I wasn’t impressed with “A drop of the good stuff.” They mention a statistic from the Water Corporation that 54% of household water use goes on the garden and then suggest installing a rainwater tank or garden bore to reduce reliance on scheme water [2]. This is certainly correct, but the article fails to mention that most of our scheme water comes from groundwater (up to 60%) [1]; the same place from which a garden bore extracts water.

The WA state government provides rebates for people to install water saving devices and

in the 2006/07 financial year, 2254 people in WA claimed the domestic rainwater tank rebate, and a further 3834 garden bore rebates were made…In the rebated households looked at, using a bore reduces consumption by about 120 kilolitres a year. For a rainwater tank the saving’s between 20 and 60 kilolitres, depending on whether or not it’s plumbed into your home. [2]

Rainwater tanks aren’t as useful in Perth as some climates because we have such a dry summer. Ben Jarvis from the Water Corporation points this out and recommends against using a rainwater tank only for the garden because it will fill and overflow numerous times in winter, then quickly run dry in summer [2]. Plumbing the tank into the house solves this problem, but most people would not consider this because of the added expense, logistics and necessary guards and filters.

If I knew nothing about garden bores and a rainwater tanks, I would think I’d be better off sinking a bore. Obviously West Australians agree because more are claiming the rebate for a bore. Brett Clugston, manager for Virgin Bores, was interviewed for the article and he’s getting in on the greenwashing (and making money in the process) by saying,
dianella plant in my new waterwise native garden, to the left is my washing machine greywater hose coiled after use

The main advantages of using a bore are that basically when you’re using ground water you’re saving the mains water. [2]

At the end of the article (and in a “Water Wise” box) it’s pointed out that even if you do install a bore or rainwater tank, you need to use water wisely and not waste it. This seems like an unimportant add-on, when it should actually be the most important aspect of any discussion on water use. With our declining groundwater levels, what would happen if the Gnangara Mound ran dry?

In Venice, Italy

from the 1930s to the 1970s, fresh water was pumped out of underground reservoirs beneath the city to supply surrounding factories. As the water was pumped out of these aquifers – which are rather like rocky sponges – their water-filled pores compressed and the ground sank. [3]

Combined with other factors this has caused Venice to slowly become inundated by the ocean. In 2004 scientists from the University of Padua developed a plan to save Venice from sinking into the sea by pumping 18 million cubic metres of seawater a year into the aquifer beneath the city [3]. The team is currently working on a pilot project to test the plan’s feasibility [4].

Even if this didn’t happen in Perth, if (when) the Gnangara Mound ran dry, other problems would occur. eg. extreme water shortages. To guard against this, we should be limiting our water use enormously. The best way to limit water use is to reuse it. While households and business should be encouraged to make use of grey water or processed black water for gardens and toilet flushing, household water use only makes up 11% of total water consumption, as reported by the Australian Bureau of Statistics in Water Account, Australia, 2004-05. Industry is the main culprit and agriculture uses 65% of Australia’s water. Some industries, such as rice and cotton, are so water-intensive [5] they would be better carried out in countries with higher rainfall.

One of the biggest users of water in Perth is Alcoa* (they also use large amounts of non-renewable electricity). Their sites at Kwinana (a southern suburb), Pinjarra and Wagerup (towns near Perth) process bauxite and alumina. Alcoa has 16 water licences: 5 groundwater licences and 11 surface water licences (for dams) [6]. This groundwater isn’t drawn from the Gnangara Mound because it ends at Fremantle. The aquifer they extract from is a finite resource, recharged from rainwater and other run-off, and probably declining in the same way as the Gnangara Mound. Once Alcoa pays $3000 per gigalitre-scale licence they can take slightly more than 2.5 gigalitres in total (I worked this out using the 3.6% mentioned below). Greens MP Paul Llewellyn said,

It’s almost a free asset to them. They’ve got dirt cheap energy and cheap water. [6]

Earlier in the year Alcoa wanted to increase their water use by an extra two to three billion litres a year because of the planned expansion of the Wagerup refinery (from my calculations this would double their water use). Alcoa’s Wagerup site manager Simon Butterworth said,

The water used at the Wagerup refinery is largely run-off on to the site. [6]

Run-off that would otherwise return to groundwater to replenish the aquifer, if Alcoa didn’t use it.

In 2006 Alcoa illegally drew 91 million litres of groundwater (3.6% of the amount they use each year). A Department of Water spokeswoman Liz Western said Alcoa was not fined by the State Government,

because the breach occurred while the company was applying for drought relief when its [dam] storage levels were low. The company passed a detailed hydro-geological assessment and was allowed to draw more water. [6]

Groundwater is recharged through rainfall. When less rainfall occurs during a drought, I would have thought overall water use should be decreased. Obviously WA’s government and Alcoa don’t think the same way I do.

The enormous profits of mining companies such as Alcoa could be utilised in paying increased prices for our precious water. Just because a commercial user does the groundwater pumping or rainfall collection themselves, doesn’t mean they shouldn’t pay for the privilege of using water which might otherwise be used in other ways. They’re using the water for commercial gain and this price may more correctly be designated a water tax, rather than a payment for the resource. If water use cost what it’s worth, companies would undertake research into water re-use and thus decrease their use (and the price they had to pay). WA’s government is so enamoured of the resource boom (more exports are all we ever need), they’re unlikely to ever increase charges to mining companies.


*Check out the banner of the Alcoa website for some impressive greenwashing.


  1. WA Dept of Water (2008) Gnangara Mound: A unique water resource.
  2. Rafferty, Margaret (2008) “A drop of the good stuff” Horizons, no.6, p.56-7.
  3. Knott, Michelle (2004) Plumbing the DepthsNew Scientist, 183(2457), p.36.
  4. Castelletto, Ferronato, Gambolati, Putti & Teatini (2008) “Can Venice be raised by pumping water underground? A pilot project to help decideWater Resources Research vol.44.
  5. Guerrera & Kleinman (2006) “Thirsty WorkThe Age, 14 Nov.
  6. Torre, Giovanni (2008) “Alcoa escapes fine on illegal use of water” The West Australian, 5 Jan, p.16.

3 thoughts on “Perth’s shrinking Groundwater

  1. Excellent post, as always, Clare. I really believe that we’re not doing enough in WA to curb our wasteful ways of using water – many of us would struggle to stick to the restrictions in place over east.

  2. Hi Clare,
    Dropped by again to read some of your interesting posts. As a hydrologists, this one interested me quite a bit. You are hitting the nail on the head. It is all about use, and how much we allow to be used.

    You might be interested in my sustainable yield posting ( from a couple of weeks ago. Sustainability is really a hard thing to nail. I still blame our affluence (and population, your other post and see my comment and worries there).

    Maybe Perth needs to seriously look at rainwater harvesting to increase recharge.

    I would therefore still go for the rainwater tank. unless you can balance your bore with more recharge.

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