I have had moments when I have told children to stop something like this - pouring water on someone else. These girls are clearly enjoying the pouring, the repetition, the sensory aspect of cool water on their arms - this is work. An adult might stop them because they assume a child wouldn't want another to pour water on her arm; because it is to loud for the teacher's taste; because there is a "keep to yourself" type rule at the sensory table.
I love seeing things in the classroom that I have never seen before. I'll share another moment that made me stop and think later today.