The phrase "blows out water" implies the act of purging trapped water. Antonyms for this phrase could be "retains water" or "holds water." In terms of the latter, it could be taken to mean that something is watertight or designed to keep water from escaping. Another antonym for "blows out water" could be "absorbs water." This would imply the opposite process of taking water in instead of forcing it out. Essentially, any phrase or word that conveys the opposite effect of purging or expelling water could be considered an antonym for "blows out water.