Reverse osmosis units are used for production of demineralized water without use of hydrochloric acid and sodium hydroxide. Among other things, the units are used in boiler houses, district heating plants, hospitals, dialysis centres, and laboratories, for process water in the pharmaceutical industry and the chemical industry, as well as in connection with humidification plants. RO units remove pyrogenics as well as bacteria and cause no wastewater problems. The units remove up to 90% of the organic substances and retain 98-99% of the salt in the water.