冰 is ice, and 水 is water, so 冰水 is ice water.
Ordering
杯 is cup (or mug or glass) and is the measure word for water (and other drinks), and 一 is one, so to order a glass of ice water, ask for 一杯冰水 (yāt būi bīng séui in Cantonese, yī bēi bīng shuǐ in Mandarin), one cup of ice water.
