Water added to a maintain or dilute a water-mud system. The added water may be fresh water, seawater or salt water, as appropriate for the mud. Make-up water volume is an important parameter in a material balance check on solids content and solids removal efficiency for a mud system. The amount of dilution strongly influences mud economics. If soft make-up water is needed, treatments to remove hardness ions should be done prior to adding the water to the mud to avoid clayflocculation and polymerprecipitation.