Swirling Blade

You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and water coming out of the weapon's hilt swirls into the wound. If the target fails to hit with an attack, a creature succeeds against a saving throw forced by the target or the target takes an action that can not trigger either of those, the target takes 1d6 cold damage, and the spell ends.

At Higher Levels. At 5th level, the melee attack deals an extra 1d6 cold damage to the target on a hit, and the damage the target takes for taking a turn increases to 2d6. Both damage rolls increase by 1d6 at 11th level (2d6 and 3d6) and again at 17th level (3d6 and 4d6).