If your teacher has just explained a tricky grammar point (don't worry, there aren't too many of those in Spanish!), and checks "¿Ha quedado claro?", your answer is "Está más claro que el agua".
"¿Ha quedado claro?" is roughly "Is that clear?" in English, and for "más claro que el agua" we'd say "crystal clear". It's not an expression that Spanish people tend to use ironically or sarcastically.
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