Areas in the Murray-Darling Basin could be used to store vast amounts of water underground and help build drought resilience, a CSIRO study has found.
Water banking - known as managed aquifer recharging - is when water is stored underground to be used later for irrigation and town water supply.
The study by Australia's national science agency, published in the journal Water, found that across the Murray-Darling Basin, there were water storage opportunities of between two and four cubic kilometres in underground aquifers close to rivers - the equivalent of between four and eight Sydney Harbours of water.
Study co-author Declan Page said the impending La Nina weather pattern - indicating a higher likelihood of rainfall - was a reminder to regional communities they had opportunities to secure water supplies before the next drought.
"Drought resilience starts well before droughts hit - it's planning and preparing by implementing practices that are water efficient and developing infrastructure that enables water conservation and storage," Dr Page said.
Recharging aquifers at times of higher rainfall, storing the water, and discharging them during droughts was a cost-effective way to manage regional water security.
"Water banking allows communities and their industries to potentially limit the economic impacts of a drought," he said.
Australia's most recent widespread drought in 2018-20 led to some towns reaching "day zero" where water supplies were exhausted, requiring water cartage for communities and businesses.
Many towns faced severe water restrictions and for some towns, the drought still had not broken.
Dr Page said water banking was an economical option in regions that had existing groundwater users.
Other water banking options exist, such as using treated wastewater or in confined aquifers, but they tended to be more expensive.
The study investigated the economic case for water banking in the Dubbo region, and proposed a solution where water was purchased from the water market at lower rates when it was plentiful.
The water was then stored underground where it does not evaporate until needed such as in a drought when water prices increase.
"This method of buying low and selling high is a way to fund the sustainable long-term operations of water banking schemes to enhance water security," Dr Page said.
The paper identified water banking opportunities for regions in the Murray-Darling Basin area, including the Warrego River, Condamine-Culgoa Rivers, Darling River, Macquarie-Bogan Rivers and Namoi River.
Each had the potential for more than 200 gigalitres of regional underground storage.
The study was part of CSIRO's work to improve Australia's drought resilience and protect regional communities, industries and the environment from droughts.
