The decision by the Alkimos Seawater Alliance to incorporate a groundwater treatment plant into the design of the Alkimos Seawater Desalination Plant in Western Australia is leading to safer, more sustainable drinking water.

ACCIONA, as Lead Constructor, is working with Water Corporation and Jacobs to deliver the Alkimos facility, which is the first desalination plant of this scale in Western Australia to use blending of treated groundwater and reverse osmosis permeate as the primary method for achieving final drinking water quality.

Post‑treatment chemicals are then applied only as required to align with the Australian Drinking Water Guidelines, allowing water quality to be optimised through design rather than chemical correction alone. 

Desalination removes organic matter and dissolved minerals from seawater, producing water that is extremely pure but corrosive and unsuitable for direct consumption. To meet drinking water requirements, desalinated water must undergo post‑treatment to reintroduce minerals such as calcium and magnesium and to stabilise pH, alkalinity and hardness. 

At Alkimos, this balance is achieved through a combination of targeted chemical injection and blending with filtered groundwater from the on‑site groundwater treatment plant. The groundwater produced is drinkable but typically considered hard by conventional standards. In most systems, this hardness would be reduced before entering the network. At Alkimos, it has been deliberately leveraged to support mineral balance in the desalinated supply. 

By using the natural hardness of treated groundwater, the project is expected to reduce overall chemical demand to achieve potable water by up to 50 percent, compared with traditional desalination post‑treatment approaches. This reduction improves operational efficiency while lowering long-term chemical use and associated handling requirements. 

The early engineering decision to include the groundwater treatment plant within the overall project design has enabled closer integration between desalination and post‑treatment processes. This integrated approach supports consistent water quality outcomes while simplifying operations as production increases to meet demand in Perth’s northern growth corridors. 

The groundwater treatment plant forms a key part of the broader Alkimos Seawater Desalination Plant, which is being built to provide a climate resilient, reliable drinking water source for Western Australia. The facility demonstrates how early engineering decisions can influence safety, sustainability and performance across the full life of critical water infrastructure. 

By embedding water quality optimisation into the design process, the Alkimos Seawater Alliance is supporting a more resilient approach to drinking water production that reduces reliance on chemicals, improves efficiency and helps ensure compliance with national drinking water standards as climate pressures and population growth continue to increase.