Desalination is the process of removing salt and other minerals from seawater to make it safe to drink. It has been used in simple ways since ancient times, but it wasn't until the middle of the 20th century that industrial-scale methods were widely available to coastal communities that didn't have enough water. Today, every day, approximately 300 million people in over 150 countries receive water from 20,000 desalination plants.

Only 2.5% of the world's surface water is freshwater, and only a small portion of that is readily available and suitable for human consumption. Desalination provides an alternative drinking water and irrigation source as climate change worsens. But ironically, it has significant environmental consequences. Desalination requires a choice between satisfying the growing human demand for freshwater resources and aggravating environmental issues.

New technology may be able to reduce these consequences. Desalination presently involves three basic categories: membrane technologies, thermal technologies (distillation), and chemical processes.

Thermal desalination boils water until it evaporates, leaving the minerals behind. The salt-free water vapor is then collected through condensation. Thermal energy for this process comes from large-scale steam generators, waste heat boilers or steam extraction from power plant turbines. One of the most common thermal procedures, multistage flash distillation (MFS), requires a facility that is easy to build and operate but is very energy-intensive.

Another method, membrane desalination, uses tremendous pressure to push seawater through small, semi-permeable membranes. These membranes permit the passage of water but keep out dissolved salts. That sounds easy, but it takes a lot of energy. The most common membrane process, reverse osmosis, was first used in the 1970s.

Desalination has many positive benefits. Specifically, in arid, drought-prone regions near saltwater or brackish water sources, desalination is a key technology, improving water security and resilience. Desalination can also help preserve environments by lowering demand on freshwater supplies like groundwater, rivers, and lakes, on which they depend. Desalination can be a reliable local source of clean water for agriculture, in addition to human use. For some highly vulnerable populations, small-scale desalination facilities in water-scarce rural areas can help ensure water security.

Desalination will certainly become more prevalent in coming years, as droughts become more severe and freshwater resources become depleted and degraded due to climate change. However, desalination has serious disadvantages as well. Stay tuned for our next episode to find out what these are and learn ways we may be able to mitigate them.

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