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Having a major headache after taking a shower, a bath, swimming or being in water for a long time. The headache usually occurs within a few minutes.
Jim: Dude, why does my head hurt so much!

Bob: Werent you in the shower ten minutes ago?

Jim: Yeah, but wh-

Bob: You have a water headache.

Jim: Ohhhhh ouch!
by Igiko Pop September 27, 2011