The West Australian Water Corporation says it will oversee the construction of a six-million-litre storage tank in Western Australia's Wheatbelt, designed to improve water quality and water pressure for outback shires.

More than 300 people in the Mount Marshall and Trayning shires will be the main benefactors of the $6.4 million project, which is due to be completed in October next year.

The Water Corporation plans to build the storage tank in Waddouring.

It is a follow-on from a $100,000 upgrade to chlorination facilities at the Trayning water treatment plant, which had already improved water quality in the area.

The $6.4 million water tank is part of a three year $32 million scheme aimed at improving water and farmland supplies in the Wheatbelt.