Cold drinking water; often refers to the glass of cold water served at restaurants.
すみません、お冷をもう一杯お願いします。
Excuse me, may I have another glass of cold water, please?
暑い日にお冷がとてもありがたかった。
The cold water was very welcome on a hot day.
セルフサービスだから、お冷は自分で用意してね。
It's self-service, so please help yourself to the cold water.
Can refer (in dialectal or older usage) to cold cooked rice (so-called 'cold rice').
昔は朝食にお冷やを食べることが多かった。
In the past, people often ate cold rice for breakfast.
お弁当に冷やを入れて持って行ったら、母は『昔の人みたいね』と言った。
When I packed cold rice in my lunchbox, my mother said, 'You seem like someone from the old days.'