Deputy Prime Minister Michael McCormack will issue a rallying cry for Australia to "get serious" about water security when he officially launches a new authority to address falling stores of urban and regional water.

The Nationals leader will on Saturday announce the $100 million National Water Grid Authority, promised during this year's federal election campaign, will be established on October 1 in a bid to drought-proof Australia "when the going gets tough again".

Deputy Prime Minister Michael McCormack: "I intend to be known as the Nationals’ leader who builds dams." Credit:Alex Ellinghausen

Water storages across the eastern states have hit their lowest mark in decades in recent months, with dams feeding both Melbourne and Sydney in need of heavy spring rains to head off further restrictions on urban households.

Water authorities have warned the downward trend in storages over the past five years reflects population-driven growth in demand and less water entering reservoirs. A changing climate, with longer drier periods, higher temperatures and drier soils have reduced stream flows into reservoirs.