Wiktionary
a. insipid, wishy-washy, weak. (from 18th c.) n. 1 (context obsolete English) A light bluish colour. (16th c.) 2 Something insipid or mawkish. (from 18th c.)
Usage examples of "milk-and-water".
That clunch Elvin writes that he will still be on his wedding trip, and George cannot leave the milk-and-water miss he married.
She might burst into tears on occasion, but she had never been a vaporish milk-and-water miss.
Yellow journalists and milk-and-water litterateurs have painted pictures of the emancipated woman that make the hair of the good citizen and his dull companion stand up on end.
Boots couldn't but feel with increased acuteness what a base deceiver he was, when they consulted him at breakfast (they had ordered sweet milk-and-water, and toast and currant jelly, over- night) about the pony.