The Mundaring Water Treatment Plant, the first fully fledged PPP in the Western Australian water industry, was officially opened by Western Australian Premier Colin Barnett on 25 March 2014. The project will supply Western Australia's Goldfield and Agricultural water system.

The project was developed on a design, build and operate basis for a period of 35 years. The project, worth A$300 million (US$277 million), was awarded to Helena Water a consortium formed by Acciona Agua, Trility (a Mitsubishi Corporation subsidiary) and an investment fund of Lloyds Bank in February 2011.

The contract was signed between Water Corporation, the main supplier of water, wastewater and drainage services in Western Australia, and the consortium in July 2011. The project also reached financial closure in July 2011. Approximately A$255m of the total funding package of A$300m was provided by the Bank of Tokyo-Mitsubishi UFJ (BTMU), Banco Bilbao Vizcaya Argentaria (BBVA), BNP Paribas and WestLB in the form of a seven-year syndicated loan.

The remaining amount was paid in the form of equity divided amongst Acciona Agua (25.05%), Trility (25.05%) and Lloyds TSB's infrastructure fund Uberior Infrastructure Investments (49.9%).

The Mundaring WTP will supply the Goldfield and Agricultural Water System, including Kalgoorlie in the State of Western Australia. The plant has an initial capacity of 165 million litres per day, and a maximum capacity of around 240 million litres per day.

The Mundaring plant will become the main source of water for 100,000 people, although it is prepared to cover the demands of a larger population in future.

Apart from the WTP the project also involves the upgrades of weir wall outlets and electrical power, improvements to the precinct and public facilities for city denizens and tourists, plus relocation of the DEC's Perth Hills District office.