There were an estimated 700 million people on Earth suffering from drinkable water scarcity in 2018 and that figure is expected to grow to 1.8 billion by the end of the next decade. One in four people live in places at high risk of running out of water.
Yet. our blue planet has plenty of water but most of it is either in form of ice (polar caps) or salty. Water distillation
is thousands of years old but it requires a lot of energy to heat the water to its boiling point. More recently engineers have developed a method to filter the water separating the salt through a membrane (reverse osmoses). This is better in energy terms but still quite expensive (it takes about 15,000 KW to get 4,500 cubic meter of drinkable water), somewhere between 0.5 and 1$ per cubic meter (in 2019 the 0.5$ per cubic meter barrier has been broken).
Now, that cost might seem negligible but you have to compare it to the cost of normal water (that is basically 0) and consider that desalinated water is not just for drinking but for agriculture (and agriculture requires a tremendous amount of water: to grow one apple it takes 70 litre of water, half a kg of chicken requires 2,275 litres of water…).
Researchers at the Berkely Lab have invented a new process to power desalination using solar energy (see graphic). By using direct solar energy they expect to dramatically cut the cost of producing drinkable water (as well as the one to irrigate fields). Rather than applying reverse osmoses their process uses ionic liquid separation through forward osmoses.
Notice, however, that this process is addressing just one part of the cost in producing water, another important factor that is often neglected, is the cost of managing the salt produced. Today, most desalination plants are simply throwing the brine (salt) back in the sea but this is in creasing local salinity adversely affecting the plancton and the whole food chain. Proper disposal of salt is costly and will have to be managed.
As with any technology there are ups and there are down. It is usually quite difficult to find a solution with no strings attached.