Pretreatment is the set of technologies used before the main purification stages. It prepares feed water by reducing contaminants that can damage or overload RO membranes, EDI modules, DI cartridges and final polishing stages.

Pretreatment is not a single technology. It may include sediment filtration, activated carbon, softening, antiscalant dosing, iron removal, pressure regulation and other steps depending on feed water quality.