What is the primary purpose of re-mineralization after desalination using reverse osmosis?

The primary purpose of re-mineralization after desalination using reverse osmosis (RO) is to stabilize the water and make it palatable and less corrosive for distribution systems. RO desalination produces water that is essentially pure H2O, meaning it lacks essential minerals like calcium and magnesium. This ultra-pure water is aggressive, meaning it has a strong tendency to dissolve metals from pipes and plumbing fixtures, potentially leading to corrosion and the leaching of harmful substances like lead and copper into the drinking water. Re-mineralization involves adding these minerals back into the desalinated water to create a stable and less corrosive product. The addition of calcium and magnesium increases the water's hardness and alkalinity, which helps to buffer the water against pH changes and reduce its corrosivity. It also improves the taste of the water, making it more palatable to consumers. Without re-mineralization, desalinated water can taste flat or bland due to the absence of dissolved minerals. Re-mineralization is typically achieved by passing the desalinated water through beds of limestone (calcium carbonate) or by adding calcium chloride and magnesium chloride. The specific minerals and concentrations added depend on local regulations and the desired water quality characteristics. Re-mineralization is a crucial step in ensuring that desalinated water is safe, palatable, and compatible with existing water distribution infrastructure.