stand-offish; distant; not frank; reserved
watery (alcohol, coffee, etc.)
そんな水臭いこと言わないで。
Don't be so distant with me.
水臭いなあ、遠慮するなよ。
Don't be so reserved, no need to hold back.
最近彼女が水臭くなった。
She's become distant with me lately.