I was facing a weird vampire dragon lord that was projecting and using his blood as a weapon and shield. He was in the process of using it to suffocate the party. In a fit of desperation, I googled "percent of water that makes up blood" and after seeing it was sufficiently high, I presented this prompt to the DM:

SO: we all know that blood is mostly water. In fact, it's x% of it (can't quite remember the amount...) So with that, I said I cast create or destroy water at 4th level to destroy 40 gallons of water from the blood

DM lets me, then says he has to roll some dice.

After a considerable amount of dice rolling sounds, he announces that the entire left side of the vampire went limp, and he fell out of the sky, dying rapidly. I saved the party by destroying some water as a 17th level encounter.