Water Manipulation (水操作 mizu sōsa, lit. "Water Operation") is an Extra Skill used by Rimuru Tempest. It represents the user's ability to manipulate water.
After Rimuru (unnamed at the time) learned Hydraulic Propulsion, Water Current Control, and Water Blade, the three Skills were fused and evolved into Water Manipulation.
After defeating Ifrit, Great Sage fused Water Manipulation with the new Extra Skills Fire Manipulation and Combustion via Unique Skill Deviant, resulting in Extra Skills Dark Flame and Molecular Manipulation.