Reverse osmosis plants have at their heart a membrane that, if damaged, reduces output, increases costs, and gives poor water quality. Hence, it is important to keep it clean and operate efficiently.

Most reverse osmosis membranes are formed from hollow fiber or thin-film composite sheets, with the membrane allowing the passage of pure water and rejecting the dissolved solids in the water.

As water passes along the membrane surface, the solids concentration increases, and some sparingly soluble salts start to exceed their solubility and precipitate. When precipitated onto the membrane surface, this causes fouling that may reduce output and increase product water conductivity. The worst of these solids are calcium carbonate and calcium sulfate, so preventing their precipitation is vital if the membrane is to function efficiently.

The traditional way to prevent this was to "de-alkalize" the water using sulphuric acid to prevent calcium carbonate precipitation. However, the hazardous acid increases the sulphates and the corrosivity of the water on both sides of the membrane. Reducing the recovery rate of the reverse osmosis plant eliminated calcium sulphate, but this reduces the efficiency of the plant and hence increases costs.