adverb, expression
like water; as if it grows on trees
Set phrase used to describe spending money or using resources freely and without restraint, often in a critical or cautionary tone. Typically appears with verbs like 使う (spend).
See also: 湯水
彼は湯水のごとく金を使う。
He spends money like water.
湯水のごとく資源を消費してはいけない。
You must not consume resources as if they grew on trees.
湯水 is the noun meaning 'hot and cold water,' but in this phrase it metaphorically represents something abundant and cheap. The full expression 湯水のごとく is the adverbial form.
From 湯水 (hot and cold water) + の + ごとく (like). The phrase likens spending to using water, which is traditionally seen as plentiful and free.