What is desalination technology?

• To convert salt water into freshwater, the most prevalent technology in the world is reverse osmosis (RO). A plant pumps in salty or brackish water, filters separate the salt from the water, and the salty water is returned to the sea. Fresh water is sent to households.
• The reverse osmosis system applies an external pressure to reverse the natural flow of solvent and so seawater or brackish water is pressurised against one surface of the membrane, causing salt-depleted water to move across the membrane, releasing clean water from the low-pressure side’. 
• Seawater has Total Dissolved Solids (TDS) — a measure of salinity — close to 35,000 parts per million (ppm), or equivalent to 35 g of salt per one litre/kg of water. An effective network of RO plants reduce this down to about 200-500 ppm. There are about 18,000 desalination plants in the world across 150 countries and nearly half of Israel’s water is sourced through desalination.

What are the problems with RO plants?

• Because RO plants convert seawater to fresh water, the major environmental challenge they pose is the deposition of brine (highly concentrated salt water) along the shores.
• Fishermen have complained that the brine being deposited along the seashore is triggering changes along the coastline and reducing the availability of prawn, sardine and mackerel. 
• Environmentalists second this saying that hyper salinity along the shore affects plankton, which is the main food for several of these fish species.
• The high pressure motors needed to draw in the seawater end up sucking in small fish and life forms, thereby crushing and killing them — again a loss of marine resource.