The source material for the production of water for pharmaceutical purposes should be water with drinking water parameters, according to locally applicable regulations. Usually, it is the Regulation of the Minister of Health on the quality of water intended for human consumption.

The state-of-art Purified Water (PW) generation process is based on membrane technologies such as reverse osmosis (RO), electrodeionization (EDI or CEDI) and membrane degassing. Membrane technologies allow for obtaining water with very good output parameters. However, they require a very carefully designed water pre-treatment system, in order to perform the following main tasks:

• Removal of suspended solids.
• Removal of iron and manganese compounds.
• Water softening or hardness stabilization.
• Removal or chemical binding of chlorine.
• Removal or chemical binding of carbon dioxide.
• Removal of colloidal impurities (to decrease value of the SDI₁₅ index).

The most popular method of generation of Purified Water that meets the quality requirements set out in the European Pharmacopoeia (Ph. Eur.) is the technology of double-stage reverse osmosis.

For the generation of Purified Water with parameters compliant with the requirements of the US Pharmacopoeia, a combination of reverse osmosis and electrodeionization techniques is most often used. Depending on the level of salinity in the raw water, the electrodionisation can be preceded by single- or double-stage reverse osmosis.