The figure ‘7.5 billion' refer to the number of litres of water ……………

Desalination, or desalting, the conversion of saline water to fresh water, is a technique that is increasingly used where freshwater supplies are insufficient. In the mid 1980s, more than 1500 desalination plants throughout the world, many of which were situated in the Middle East, were producing a total of more than 7.5 billion litres of fresh water per day from saline waters. Desalination is accomplished through distillation, freezing, demineralisation by ion exchangers, electro dialysis, or reverse osmosis.