The most efficient solution to the problem of preventing contamination of the reservoirs with waste water is their reuse for water supply of the borehole. Requirements are presented which the purified waste water must meet. As a result of the conducted studies it has been established that in reservoirs, only coarsely dispersed mixture, weighting compounds and floating petroleum products are removed from the water. Finely dispersed suspension and colloid particles have a sedimentation stability and do not settle out under the influence of the gravity force. For drilling waste water there is a characteristic inconsistency in the degree of contamination both at the different boreholes and at one borehole with the passage of time. Physical-chemical characteristics of the waste waters are presented. The greatest degree of contamination of water is observed when such operations are performed as replacement of the drilling fluid, lifting of the drilling tool, cementing as well as the development of emergencies. Studies on the purification of drilling water were conducted on an experimental-industrial unit.