Initial water treatment in the lab could start with a water filter to remove particulates followed by reverse osmosis. Reverse Osmosis removes >94% of dissolved ions and >99% of suspended solids, bacteria and pyrogens. Reverse osmosis produces Type III water ready for further purification to Type II or Type I water. The amount of contaminants removed depends greatly on the feed water.
Osmosis is the tendency of water molecules to move across a semi-permeable membrane from the purer side of the membrane to the less pure side; this is how cells exchange water and nutrients. Osmotic pressure is the pressure of the water molecules on the membrane from the purer side. In reverse osmosis pressure is applied – greater than osmotic pressure – to the less pure side of the membrane forcing water across the membrane and leaving behind most of the inorganic ions and other contaminants.
Particulates, dissolved organics, and Chlorine are damaging to reverse osmosis membranes and many RO units have a pre-filter and an activated carbon filter. Reverse osmosis has a slower flow rate than other water treatment technologies so it is necessary to store the RO water in a tank. A pump may also be necessary to provide the required flow rate from the RO tank to subsequent water treatment units.
RO is a good first step in a water polishing system; the quality of RO water protects polishing systems such as deionizing cartridges. RO water quality is sufficient for many routine laboratory needs.