Before the pandemic, we worked with a design institute in Henan on a water plant project with a daily treatment capacity of 80,000 tons. The raw water here had a hardness of 450 mg/L. At first, the design institute planned to use reverse osmosis (RO) membranes to solve the high-hardness problem. But we told them clearly: RO membranes have no advantages when dealing with such highly hard water.

Strictly speaking, the strength of reverse osmosis membranes lies in separating dissolved salts, rather than being the best choice for hardness removal. From the perspective of RO membrane operation, the influent water hardness should be kept below 50 mg/L. If the value goes higher, the membranes will get clogged quickly and stop working properly.

For large-volume water projects with high hardness, the lime-soda ash softening method is a more cost-effective choice in terms of both treatment results and overall costs.

For small industrial or commercial sites, sodium ion exchange softening is more economical for hardness removal.

Now let’s get back to our main question today: Can reverse osmosis membranes remove water hardness?

The answer is yes, but only when water hardness is below 50 mg/L. If the hardness exceeds this value, you should not consider RO membranes at all.