水

水 (shuǐ) is the Chinese word for 'water' — the substance, drinking water, and water more broadly (rivers, lakes, rain). Unlike English, Chinese speakers always count water with a measure word: 一杯水 ('a glass of water'), 一瓶水 ('a bottle of water'), 一口水 ('a sip of water') — never *一水. Two useful distinctions for restaurants: 开水 (kāishuǐ) is 'boiled / hot drinking water,' the default beverage in many Chinese households; 冰水 (bīngshuǐ) is 'ice water,' which you may need to specifically request. 水 is also a productive component in compounds: 水果 (fruit, lit. 'water fruit'), 喝水 (drink water), 洗手水 (water for washing hands). The character 水 is one of the basic 部首 (radicals) and appears reduced as 氵 (three drops) in many other characters: 河 river, 海 sea, 酒 alcohol.

Memory hook: 水 is a pictograph — the central line is the river, the curves on each side are splashing droplets.