He can keep control of himself  even if say, you put him in a cup and poured half of him out he can try and get back together though if the walls of the cup were too high/steep I guess he'd be stuck in that form. But as far as other liquids go, like I said he can join and move through them. Guess I should clarify he stays himself. He's not gonna melt into the ocean and come back as a giant or anything. He'll become himself again and the extra water will run off him like always. Guess think of him more like a sentient puddle of something between oil and water. He never quite joins with them but moves through them just fine and can slip around on the floor.