Numerous technological processes require extremely clean water. Such water is used among others in pharmaceutical, cosmetic, food, electric and energy industry, as well as in laboratory analyses, air-conditioning engineering and health care. Water demineralization can be conducted in reverse osmosis process. Under high pressure raw water goes through a permeable membrane which separates two solutions of different concentration. Clean water molecules go through the membrane, whereas salt and other contaminants, such as colloids and bacteria, are drained to sewage system.