This article is to elucidate the rules and procedures in force required and determining the cost of processing one cubic meter of water applied in a water treatment plant of Santiago de Cuba province. This calculation will allow the Aqueduct and Sewer Company (EAAL) “Aguas Santiago” measure efficiency in the technological process of water purification , charting a policy of maintaining the infrastructure that allows provide a stable supply of drinking water and serve as a basis for price formation in the collection of the service.