Abstract: In a process and apparatus for obtaining sterilized and bacteria-free water suitable for medicinal injections and other purposes, deionized water is supplied to a reverse osmosis filter, which is impervious to attack by bacteria and which is arranged such that its entire surface may be sterilized, to obtain a sterile permeate and a portion of the deionized water supplied to the filter is recycled. The recycled portion of deionized water may be recycled through the deionization plant from which it is derived or through a closed circuit and may be recycled in combination with the sterile permeate.