Technical and mineral level effects of water treatment, corrosion control

Hard water with salts of Ca and Mg may cause scaling, and is often softened. Water with toxic substances, e.g. heavy metals, is harmful, and is often treated with different filtering methods, nowadays often reverse osmosis (RO). There are more than 21,000 desalination plants around the world, providing more than 350 million people with drinking water, and there are more to come. RO-treated waters without pH-adjustment tend to be corrosive; causing elevated levels of metals released from especially pipes, e.g. Pb, Fe and Cu, but also lack minerals, causing decreased daily intake and loss of minerals from the body. Even pH-adjusted RO water has very low mineral content. Food boiled in such water also tends to lose minerals. There are indexes to be used as guides to choose a re-mineralization method after RO. However, methods used today don’t take mineral levels in treated drinking water preferable for human consumption into account, as corrosion aspects are only considered. Treatment with dissolution of dolomitic-calcitic limestone (free from toxic elements) giving 30-80 mg/L Ca, 100-300 mg/L HCO₃, 10-50 mg/L Mg and 25-100 mg/L SO₄, with Ca/Mg 2-3:1 would be preferable for drinking water production.