The accepted school of thought has long been plants primarily limit water loss by closing tiny pores in the skin of their leaves.
In doing so they also limit their uptake of carbon dioxide, which is bad news for food production because a lack of CO2 slows down photosynthesis, which in turn hurts growth rates and yields.
But Australian scientists have discovered some important cropping plants have another way to control water loss.
They use the membranes of mesophyll cells, found inside leaves, to regulate water.
The mechanism kicks in when the environment is dry and allows plants to reduce water loss with little effect on CO2 uptake.
Dr Chin Wong from the Australian National University led the research and says it's a "dream discovery" that should help plant breeders develop more water-efficient crops down the track.
"The agriculture industry has long held high hopes for scientists to come up with a way to deliver highly productive crops that use water efficiently," he says.
"Plant scientists have been dealing with this big question of how to increase CO2 uptake and reduce water loss without negatively affecting yields.
"Having this mechanism that can reduce water loss with little effect on CO2 uptake presents an opportunity for agricultural scientists and plant breeders researching ways to improve water use efficiency and create drought-tolerant crops."
The research found the membrane mechanism in a dozen plant species including sunflowers, beans and cotton.
Dr Wong says more work needs to be done to establish if all plants have the mechanism, but believes it could be common in fast-growing plants including food crops.
Droughts are more frequent and fierce in all regions of the world due to climate change, making the pursuit of more resilient food crops an international imperative.
ANU researcher Diego Marquez, who co-authored the study, says the next step will be working out how to manipulate the mechanism and use it to breed more water-efficient crops.
"Now that we've identified it we have to see how we can exploit it. (That means) more research, of course, but we are very confident it's going to have an impact if you want to breed plants that are more drought resistant."
Another ANU co-author, Distinguished Professor Graham Farquhar, hopes the discovery will prompt a wave of investment.
"We expect that both government and industry will see the value of contributing funds to achieve this goal," he said.
The research also involved scientists from James Cook University. It has been published in the journal Nature Plants.
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