Back then, coastal Aboriginal people turned to rivers, streams and lakes for drinking water; those inland, perhaps a mound spring or well-charged rock hole.

Others may have had to collect dew, scoop water from a claypan after rain, or dig a soak in a dry sandy riverbed.

As earth’s second driest continent, Australia’s annual rainfall totals just 474mm (averaged across the nation for 2021-22). Only Antarctica receives less.

It’s no surprise then that “will we have enough water?” remains a question for postcolonial Australia as well.

Today, as the availability of surface water shifts under climate change, modern water authorities are searching for new sources of water, ways to save it, or the means to make its systems of capture, storage and delivery more efficient.

On the coasts – where 80% of Australians live – surface water sources still rule. For inland Australia, groundwater remains king.

But such well-drawn lines are blurring under climate change.

According to Australia: State of the Environment 2021, there has been “increased dependence on groundwater and an increase in widespread water restrictions in many regions of Australia”.

In response, the Australian water industry is undergoing profound change. To see just how profound, and for a taste of how Australia’s water future might look, consider our south-west corner.

When rainfall dries up

Since 1975, the average inflow to Perth’s drinking water dams has plummeted from 420 GL (gigalitres or billion litres) each year to a currently anticipated 25 GL.

Rainfall declined 10-25% over the time, causing groundwater levels to fall in the Perth Basin, the water-bearing geological structures underlying the region.

“At first the decline in the western area was thought to be natural variability,” say WA researchers investigating the phenomena and published in the Journal of the Royal Society of Western Australia.

It was not until the mid-1990s, when runoff into the dams that supply Perth became unreliable, that climate change was considered a factor.

“Climate projections indicate a continuing drying trend is likely with increased temperatures and possibly a greater proportion of annual rainfall, and therefore flood risks, in summer.”

If correct, the predictions for the south-west mean water yields in WA dams and aquifers will continue to decline.

Such findings, as well as earlier measurements and research, have driven WA water planners to carefully reexamine the region’s groundwater sources to stem the loss.

The sedimentary aquifers of the Perth Basin extend along the Swan Coastal Plain from regional Busselton about 220km southwest of Perth to north of Geraldton, and constitute the state’s biggest and most important source of fresh water.

More than 85% of the state’s population live above. And groundwater now meets 70% of their water needs.

But desalinated seawater and recycled water are also in play, and in ways you might not expect.

In 2023, Cosmos put questions on water planning under climate change to the WA Department of Water and Environmental Regulation (DWER), which manages and regulates the State’s water resources. Experts from the department response in writing from a spokesperson.

“Over the past two decades,” the spokesperson writes, “planning for water supply security in Western Australia’s South-West land division has reflected the effects of reducing rainfall due to climate change on decreasing availability of surface water and groundwater resources and the growth of the State’s population and economy.

“Seawater desalination can now meet almost half of the total water needs for Greater Perth’s potable water supplies.”

The seawater and recycled water form part of a shift in thinking on water.

In late November, the WA Government launched its Western Australian Climate Policy, aiming for “a climate-resilient community and a prosperous low-carbon future”.

At the same time, it launched Rebalancing our Groundwater to “invest in sustainable, climate–resilient water sources”.

What is climate-resilient water?

In 2020, at the Sydney University conference Running Out of Water, former NSW Water Minister Melinda Pavey told the audience that (in) regional New South Wales 12% of the total water supply is derived from recycled water.

“I think there’s a greater understanding and respect of water within our regional communities,” she says.

“Whether it’s from our farming practices, [or] a lot of people still get their water from their own personal tanks, [it] has given us an opportunity to take some of those learnings and have those conversations with the city.”

Pavey was flagging a shift in thinking on water, something brewing among water scientists and planners for some time. One such shift is the idea of climate-resilient water.

The Bureau of Meteorology defines sources of climate-resilient water as those on which variation in rainfall and temperature has little or no influence

In 2015, the BOM launched its Climate Resilient Water Sources web portal to provide a national snapshot of where such sources might be found. By definition, the mapping includes only desalinated and recycled water sources.

But online portals aside, and as Pavey intimates, Australia’s regions are where much of the bricks and mortar innovation in climate resilience can be found.

Can aquifers save the day?

Australia boasts three major groundwater basins. The Great Artesian Basin waters one-fifth of the continent’s dry interior, the alluvial aquifers of the Murray–Darling Basin support Australia’s major food bowl, and Perth Basin provides water to Perth and regions.

Smaller aquifers sustain communities and economies elsewhere across the country.

Surface water flows, especially from big storm events, usually recharge our groundwater storages; so if they decline, groundwater levels suffer.

Groundwater then is not – in and of itself – a panacea for the problems water resources managers face.

Better knowledge needed to conserve groundwater

Threats to our groundwater resources are many, including fragmented regulation, a lack of planning, and threats from mining, all on top of physicochemical issues like salinity and contaminants.

Pumping from aquifers causes water tables to fall, which can affect groundwater-dependent ecosystems (GDEs), neighbouring users, flows in nearby rivers, and levels of salinity.

Furthermore, over-pumping of groundwater may not be detected for several decades due to the geologically slow rates at which groundwater flows and recharges.

Per- and poly-fluoroalkyl substances, or PFAS from firefighting foam, has contaminated some groundwater supplies, particularly air force bases.

Over the past year alone, Cosmos reported on a call from Australian scientists for better management of our groundwater, an 800-year low in aquifers of our south-west, falling levels of groundwater in bores across the nation, and a similar result from recent computer modelling of the Murray Darling Basin.

Fortunately, several clever techniques are on hand.

Managed aquifer recharge

A technique proving successful in the Murray Darling Basin is the purposeful recharge of aquifers as insurance against drought. This can be for environmental purposes, or to save water from a good season, for one when conditions are dry.

Called managed aquifer recharge, the method stores water underground in natural reservoirs. Also sometimes called water banking, the alternative handle can refer to water for agriculture.

MAR techniques use infiltration ponds to recharge unconfined aquifers, or injection wells to recharge deeper confined aquifers. The techniques can store natural surface or groundwater, recycled water (stormwater, industrial or wastewater) or desalinated seawater.

CSIRO has developed a map of water banking projects in regional locations around the country. One site – Australia’s first full-scale Groundwater Replenishment Scheme  is also in Perth.

Says the DWER spokesperson: “In 2017, the Beenyup Groundwater Replenishment Scheme started injecting highly treated wastewater into Perth’s deep aquifers for subsequent abstraction.

“The State Government also applies strict permanent demand management measures, including a total sprinkler ban over winter in some parts of the state, including the Perth area.”

Purified beyond drinking water standards, the treated wastewater recharges the groundwater, bolstering water security.

Another site of improved water security is the Manjimup-Pemberton area. In August, after investigating a January 2023 report by the Southern Forests Irrigation Scheme Group, the WA Government pledged $15m to improve water security there for horticultural growers.

The report recommended water security in the region be managed at the individual farm level, which meant directing funding to enlarge existing dams and improve stream monitoring, rather than promote large infrastructure.

A water banking scheme was also investigated to allow water entitlement holders to store unused water allocations for the following season.

Historically speaking, Perth was also host to Australia’s first large-scale seawater desalination plant, completed in November 2006, a forerunner to more than 30 plants now operating across the country.

The result, DWER advises, is that around 9,000 businesses and industries and 200,000 households now self-supply about 650 gigalitres per year of groundwater via their own bores and infrastructure.

More than 1,000 gigalitres per year of water is used across the Basin, comprising about 200 gigalitres of surface water, 145 gigalitre from seawater desalination, and 25 gigalitres of recycled wastewater.

By recharging aquifers and diversifying its sources, Perth has moved from a water crisis to smoother sailing. And others are doing similarly, including MAR schemes at inland Broken Hill, NSW and urban Salisbury, SA. Stormwater also has great potential, including for drinking water.

So. Will we run out of water? Not while science holds sway.