The paper deals with water conditioning issues in oil-field development using water-flooding. It is common knowledge that injected water contains oil residues and mechanical impurities, which affect permeability of geological horizon. It has been shown that these water impurities could intensify rock colmatation up to a full clogging of pores and fractures. Hence, issues of improving quality of injected water, aimed to ensure enhancement of reservoir properties, have been studied from a variety of new angles. There are given results of conducted test experiments as well as detailed description of elaborated equipment design. It has been established that two-stage treatment technology proposed in the paper, by making use of magnetic treatment device and sewage tank with liquid hydrophobic layer, will allow to considerably improve quality of injected water. Suggested water treatment unit appears to be highly applicable, providing a maximum effect at a minimum material cost.