Reverse osmosis involves water treatment and thus one of the most important questions related to the future.
Water is mechanically pushed through a semipermeable membrane with ultrafine pores in one direction. This separates particles at a molecular level. Water molecules can pass through the membrane, while other substances, such as bacteria, viruses, calcium deposits, salt, heavy-metal compounds, and drug residues, are removed. Unlike osmosis, reverse osmosis aims for the greatest imbalance possible between the two sides rather than balance.
The process was first used in the 1960s in the United States. At the time, NASA was looking for a potable-water-recycling system for manned spaceflights. On earth, desalination, among other methods, is used to provide dry regions with drinking water from saltwater. Given the rising expectations for the quality of drinking water and the expected shortage of potable water in the coming decades, even in urban areas, reverse osmosis is becoming more important. To date, it is the most effective process for purifying water and, unlike forward osmosis, does not require the use of chemicals.
Unfortunately, it is very energy intensive and, in some cases, can put a strain on the environment. For example, the desalination process results in a large amount of brine waste, which is diverted back to the sea and thus increases its salinity. The consequences of this for the environment are not clear.