You're stuck in a prison on the sun with nothing but a spoon. Lucky for you a tsunami is coming, so you take your spoon and use the tsunami to quench your thirst. You spoon the hot, hot water into your mouth as fast as you can. This is the only way to get water on the sun.
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?
Currently there are no similar looking kanji which exist in the WaniKani learning system