Shamita was seen asking KK & Umer in the kitchen why they did they not use water in Prateik- Shamita task to extract reaction. She further said I would have won had you guys used water. At that point I heard Umer saying & I quote" mujhe pata hai woh paani le hi nahi sakta"
So when he threw water on Prateik under the guise of throwing it on Rashmi, he did that deliberately to instigate P as he knew he can't stand getting wet. Otherwise why was he throwing water on Rashmi at all.
And when Prateik retaliated by throwing water at him, he was the one who lost his cool & got physical. So don't do unto others what you can't take. He tried to dig hole for Prateik and fell in it himself.
What goes around comes around.