Methods for conserving the use of fresh wash water in crude oil desalting are described. A crude oil stream including salt mixes with a wash water stream to form an emulsion. The emulsion flows to a desalter, and the wash water coalesces to reform the wash water stream and to transfer at least a portion of the salt from the crude oil stream to the wash water stream. The crude oil stream with reduced salt content separates from the wash water stream. The effluent, which includes the wash water stream, flows from the desalter to a processing unit. The effluent is processed to reduce a concentration of salt in the effluent to be substantially equal to or less than a concentration of salt in the wash water stream. At least a portion of the processed effluent mixes with the crude oil stream before the emulsion flows to the desalter.