water warmed in the sun
Refers to water that has been left in sunlight and become lukewarm, often with a slightly negative nuance of being stale or unpleasantly tepid.
Water left in the summer sun is lukewarm and not very tasty.
Standard kanji spelling.
Search-only form; not a standard written variant.
Compound of 日向 (ひなた, 'sunny place') and 水 (みず, 'water').