Questions of water treatment in order to hold the environmental stability of the farm landscape based on irrigation systems are considered. The question on the necessity to control the ion composition and total mineralization of irrigation water in order to directly improve physical and chemical properties of soils at irrigated areas, lowering the risk of their salinization and alkalinization, and holding the environmental stability of farm landscape, is brought up. The methods of directed varying the quality of irrigation water in technologies of its controlling are presented. The advantages of the method of the reverse osmosis compared with other separation methods of the ion composition of water and the essence of the membrane method are determined. When implementing this method, the component composition of water varies at a molecular level. The schematic of the installation for the water quality control, using which, water of various ion compositions and required quality for several consumers; notably, for the drop or intrasoil irrigation, drinking water supply, and technical needs; is presented. The reasonability of this method of water treatment; which provides a decrease in expenses for the treatment of water entering soil moistening, preparation of water of a definite quality for the multipurpose use, and promotes a decrease in the anthropogenic effect on the surrounding medium; is substantiated.