cold water; cold drinking water
Refers to cold water, often for drinking. Can also appear in set phrases like 冷や水を浴びせる (to throw cold water on, to discourage).
Cold water tastes good in summer.
He said something that threw cold water on the proposal.
Compound of 冷や (hiya, 'cold') + 水 (mizu, 'water'). The reading ひやみず is a straightforward combination.