to fish in the air
... spend money llike water挥金如土 to fish in the air水中捞月 All good things must come to and end天下没有不散发的宴席 ...
make vain efforts
水中捞月
"水中捞月"是个多义词,它可以指水中捞月(中医名词),水中捞月(汉语成语)。