You're stuck in a prison on the scorching hot sun with nothing but a spoon. Lucky for you, a tsunami is coming, right as you can feel yourself completely dry up. So you take your spoon and use the tsunami to quench your thirst.
This method of quenching your thirst reminds you of being in a car wash (かわ). The water pours over you in waves, and you're stuck inside a metal cage. Totally the same thing as a car wash, right?