Global demand for fresh water is set to outstrip supply as a result of population growth by the middle of this century if current levels of consumption continue, a study said.

Fears of water shortages could intensify although this is not the first time in history that demand is poised to outpace supply, Tony Parolari, the study’s lead author, said on Wednesday.

“Global water consumption per capita has been declining since 1980 which means efficiency is increasing,” Parolari, a researcher at Duke University, told the Thomson Reuters Foundation.

“But if population growth trends continue, water use will have to decline more substantially.”

The world’s population is expected to hit 9.6 billion by 2050 from more than 7 billion now, according to U.N. estimates.

Whether humans can adapt to declining water supplies depends on what new technologies for finding water are developed, and whether population growth levels off, the study said.

The paper, published in the journal WIREs Water, analyzed historical information on water consumption and demographics with the help of mathematical models to chart changes over time.

Shortages are already affecting millions in Sao Paulo, Brazil, where residents have been hoarding water in their apartments following a drought, and the U.S. state of California which is entering its fourth year of drought.

In past eras of water scarcity, during the expansion of European cities such as London and Paris in the 19th and early 20th century, technological solutions to the problem were developed - such as expanding pipeline networks to pump in water from further afield.

Current pressures could be solved or at least mitigated with new expertise, including improved ways of removing salt from ocean water to produce fresh drinking water, Parolari said.