Desalination and a drying climate

Call him Danny. His family has grown carrots, cauliflowers and salad greens on the sandy soils north of Wanneroo for four generations, watering every row from a private bore sunk into the Gnangara groundwater system that sits beneath Perth's northern suburbs. His father used to hit water at around twelve metres; Danny drills closer to twenty now, and the market garden two properties over closed a few years back when its own bore ran dry in late summer. Twenty-five kilometres to his south-west, past the pine plantations and the new housing estates chewing into what used to be bush, Water Corporation crews are threading a $2.8 billion desalination plant into the dunes at Alkimos — the newest and largest attempt yet to solve, at the coast, a water problem that started inland, underground, and in a sky that no longer rains the way it used to.

What the government did

Western Australia was not pushed into desalination by a single drought; it built the practice into policy nearly two decades ago, once it became clear the south-west's declining rainfall was not a passing cycle. The Perth Seawater Desalination Plant at Kwinana, on Cockburn Sound south of Fremantle, opened in 2006 — the first large-scale seawater desalination plant built to supply an Australian capital city — with capacity to produce around 50 gigalitres (GL, billion litres) of drinking water a year (Water Corporation, Perth Seawater Desalination Plant, current). A second, larger plant, the Southern Seawater Desalination Plant at Binningup, was set in motion under the state's 2009 "Water Forever" fifty-year water strategy and opened in September 2011, reaching its full capacity of around 100 GL a year by January 2013 (Water Corporation, Water Forever: Towards Climate Resilience, Oct-2009; Water Corporation, Southern Seawater Desalination Plant, current). Together the two plants can supply around 45% of Perth's scheme water at full output (approx.); in practice, Water Corporation reports that desalination has provided somewhere between 30% and 40% of Perth's drinking water in any given recent year, with its share rising in the driest years as dams and groundwater give up a smaller load (Water Corporation, "Perth's unique water source mix," May-2024).

Roger Cook, who became Premier in June 2023, inherited that two-plant system and chose to extend it rather than treat it as a ceiling. In December 2023 his government confirmed a $2.8 billion program to build a third plant at Alkimos, in Perth's north, with Acciona and Jacobs Group Australia contracted, as the "Northern Water Partnership" alliance, to design, build and operate it; enabling works began in late 2023 and full construction in mid-2024 (WA Government, "$2.8 billion investment to secure Perth's next major water source," media statement, 4-Dec-2023; Water Corporation, Alkimos Seawater Desalination Plant, current). Stage 1, due to deliver first water in 2028, adds 50 GL a year of capacity — enough, Water Corporation says, to fill Perth's Optus Stadium fifty times over — with a second stage able to double that to 100 GL if required. Alongside the plant, the government has committed to contracting 400 megawatts of new wind and solar generation to power Alkimos and the two existing plants, as part of Water Corporation's target of net-zero emissions across its operations by 2035 (Water Corporation, Alkimos Seawater Desalination Plant, current). It did not stop there: the State Budget handed down on 7 May 2026 set aside a further $57.3 million to plan and investigate a fourth Perth desalination plant beyond Alkimos, alongside $606 million committed to doubling the separate Dampier Seawater Desalination Plant in the Pilbara to 8 GL a year (WA Government, 2026-27 WA State Budget, Budget Paper — Environment, 7-May-2026). Desalination, on the government's own program of works, is no longer an emergency response but the default way Western Australia now adds water supply.

The evidence

The scale of the shift is visible in Water Corporation's own long-run streamflow records, gauged since dam monitoring began in the early twentieth century. Average annual inflow into Perth's dams sat around 420 GL a year before 1975; by the driest recent year, 2010, that had collapsed to around 12 GL, and the average since 2010 has settled at roughly 76 GL a year — about a fifth of the historical baseline (Water Corporation, "Wet winter belies true impact of declining streamflow to Perth dams," 17-Sep-2025). The relationship between rainfall and runoff has itself changed: Water Corporation notes it once took about 100mm of rain to generate 10 GL of streamflow into the dams, and now takes roughly 500mm, because drier catchments absorb far more of each rain event before any of it reaches a river. Dams that once supplied most of Perth's water now contribute a residual share of scheme supply.

The cost of manufactured water

None of this manufactured water is cheap, and the bill is only beginning to be paid. The Alkimos program alone is a $2.8 billion outlay, sitting inside a $6.4 billion four-year capital works program across Water Corporation, Aqwest and Busselton Water that the 2026-27 State Budget funds with $2.7 billion in the coming financial year — on top of $606 million for the second-stage Dampier desalination plant in the Pilbara and a further $57.3 million just to plan and investigate where Perth's fourth plant might go (WA Government, 2026-27 WA State Budget, Budget Paper — Environment, 7-May-2026). Ratepayers cover part of that directly: the uniform household water service charge rose to $296.89 for 2025-26, with water-use and service charges up 2.75% across the board and sewerage charges capped at a 12.75% rise following a Landgate property revaluation (Water Corporation, Annual water use and service charges increase, 2025-26). The Economic Regulation Authority, which oversees Water Corporation's costs and tariffs under the Water Services Act 2012 and has run periodic efficient-cost inquiries since the 2000s, completed an asset management system review of the utility's water services licence in 2025 (ERA, Asset Management System Review, Water Corporation Licence WL32, 2025) — but the Alkimos investment itself was a direct government decision, not one tested through a full ERA efficient-cost inquiry before the contract was signed.

Desalination is also the most energy-hungry water WA produces. Reverse osmosis — forcing seawater through membranes fine enough to strip out salt — typically uses in the order of four to five times as much electricity per kilolitre as treating brackish groundwater (approx.; industry engineering estimates), and the Kwinana plant alone draws around 180 gigawatt-hours of electricity a year (Utility Magazine, "Water Corporation powers towards net zero future," 2024, citing Water Corporation figures). Water Corporation offsets that load not by wiring the plant directly to a turbine, but by matching it against renewable generation on the shared grid — principally the 80-megawatt Emu Downs Wind Farm, which produces around 270 GWh a year, more than the Kwinana plant consumes. That grid-matched offset, and the further 400 MW of wind and solar contracted for Alkimos, is a genuine decarbonisation commitment, and it means WA's expanding desalination fleet is not simply new gas-fired demand. But it is still new demand: every additional gigalitre of manufactured water adds load to a power system the government is simultaneously trying to decarbonise for everything else, and the renewable capacity earmarked for desalination is capacity that is not then available to displace coal and gas elsewhere in the South West Interconnected System.

The critique

The gap in the government's own account is what happens underground while the coastline gets more machinery. Groundwater still supplies roughly 30-40% of Perth's scheme water, but the aquifer it is drawn from is failing under the same rainfall decline plus decades of abstraction: the Gnangara Mound's water table has fallen by up to 10 metres since 1980, a loss of around 1,000 GL of storage, and more than half of the 30 sites the state uses to monitor groundwater-dependent wetlands are now breaching their minimum safe levels, with cave pools and wetlands in Yanchep National Park drying out (WA Government, Gnangara groundwater allocation plan, Feb-2023; WA Government, "Rebalancing our groundwater," current). The government's response — cutting Water Corporation's groundwater abstraction by around 27% by 2028 and trimming garden-bore watering rosters to save a further 30 GL a year — is a genuine acknowledgment that the aquifer cannot keep absorbing demand the way it has. But it is also an admission that the other traditional half of Perth's water supply is now shrinking at the same time as dam inflows are, which leaves desalination doing double duty: replacing water that used to fall as rain, and also replacing water the state itself is choosing to stop pumping from the ground for environmental reasons.

Desalination has drought-proofed Perth's taps; it has not drought-proofed Perth's water bill, or the aquifer under its northern suburbs.

Every plant built to close that gap is also a long-lived, capital-intensive asset that has to be financed and powered for decades regardless of how much rain falls in any given year, which locks a growing share of WA's water strategy — and its budget — into a single, expensive technology rather than a mix that develops demand management, recycling and groundwater recovery in equal measure. The 2009 Water Forever plan that set WA on this path also targeted 30% wastewater recycling by 2030; the Groundwater Replenishment Scheme at Beenyup, the main vehicle for that target, reached a combined recharge capacity of 28 GL a year after a $320 million second stage completed in 2022 — useful, but still a fraction of the roughly 150 GL a year the two seawater plants alone can produce, and only around 3-8% of Perth's total supply (Water Corporation, "$320m investment doubles Perth's rainfall-independent water source," media release, Aug-2022; Water Corporation, "Perth's unique water source mix," May-2024). Every dollar and every renewable megawatt committed to a fourth desalination plant is a dollar and a megawatt not spent scaling up the cheaper, less energy-intensive recycling option the government's own strategy nominated as a parallel priority sixteen years earlier. For a market gardener like Danny, none of that changes the fact that the water now reaching Perth's taps is safer from drought than at any point in the city's history — but it does mean the groundwater under his own bore is being managed as a shrinking, separate problem, its recovery measured in decades, while the desalination bill comes due in the next state budget.