Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions. In reverse osmosis, an applied pressure (ranging from 200 PSI to 1000 PSI) is used to overcome osmotic pressure. Reverse osmosis can remove many types of dissolved and suspended chemical species as well as biological ones (principally bacteria) from water, and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective", this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as solvent molecules, e.g., water, H₂O) to pass freely. The product water can range from 70% down to 40% depending on the amount of dissolved solids that you start with. The remaining water is a concentrated waste that must be disposed of. These can be designed for hazardous area applications or locations that are categorized as “non-hazardous” areas.