The currently available reverse osmosis, nanofiltration, and ultrafiltration membrane technologies can be used in the solution of different problems related to the treatment of strongly polluted waters of different origin and the reuse of effluents. Nevertheless, experience in the operation of membrane facilities shows the existence of specific problems due to membrane fouling and measures for its averting. As a result of the extensive studies of the mechanisms of scaling, a new approach was proposed to decrease the fouling of membranes, which consists in the improvement of the construction of a membrane channel and in the selection of membrane characteristics. The developed design of open-channel spiral-wound modules makes it possible to exploit membrane units almost without the danger of scaling and to create new effective water treatment technologies on this basis. Long-term studies and pilot tests made it possible to develop a procedure for the optimization of membrane unit operations with minimum expenditures on electric power, maintenance, and effluent discharge.