A method comprising: - mixing a crude oil stream comprising brine with a wash water stream to form an emulsion of wash water in crude oil; - flowing (203, 301) the emulsion to a desalter; - in the desalter: - coalescing the wash water 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, and; - separating a crude oil stream with reduced salt content from a desalter effluent comprising the wash water stream to which at least the portion of the salt is transferred; - flowing (207, 305) said desalter effluent to a processing unit; - in the processing unit: - processing (209, 307) the desalter effluent to form a processed effluent having a concentration of salt which is equal to or less than a concentration of salt in a fresh water stream (180, said fresh water stream having a lower salt content than the brine in the crude oil stream; - recycling (211, 309) at least a portion of the processed effluent and mixing it and the fresh water stream with the crude oil stream before flowing the emulsion to the desalter. - mixing a crude oil stream comprising brine with a wash water stream to form an emulsion of wash water in crude oil; - flowing (203, 301) the emulsion to a desalter; - in the desalter: - coalescing the wash water 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, and; - separating a crude oil stream with reduced salt content from a desalter effluent comprising the wash water stream to which at least the portion of the salt is transferred; - flowing (207, 305) said desalter effluent to a processing unit; - in the processing unit: - processing (209, 307) the desalter effluent to form a processed effluent having a concentration of salt which is equal to or less than a concentration of salt in a fresh water stream (180, said fresh water stream having a lower salt content than the brine in the crude oil stream; - recycling (211, 309) at least a portion of the processed effluent and mixing it and the fresh water stream with the crude oil stream before flowing the emulsion to the desalter. - coalescing the wash water 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, and; - separating a crude oil stream with reduced salt content from a desalter effluent comprising the wash water stream to which at least the portion of the salt is transferred; - flowing (207, 305) said desalter effluent to a processing unit; - in the processing unit: - processing (209, 307) the desalter effluent to form a processed effluent having a concentration of salt which is equal to or less than a concentration of salt in a fresh water stream (180, said fresh water stream having a lower salt content than the brine in the crude oil stream; - recycling (211, 309) at least a portion of the processed effluent and mixing it and the fresh water stream with the crude oil stream before flowing the emulsion to the desalter. - processing (209, 307) the desalter effluent to form a processed effluent having a concentration of salt which is equal to or less than a concentration of salt in a fresh water stream (180, said fresh water stream having a lower salt content than the brine in the crude oil stream; - recycling (211, 309) at least a portion of the processed effluent and mixing it and the fresh water stream with the crude oil stream before flowing the emulsion to the desalter.