石灰水(limewater)是氢氧化钙的饱和溶液的通俗名称。氢氧化钙，即Ca(OH)₂，微溶于水（25°C时溶解度为1.5 g/L。）纯石灰水是无色澄清的溶液，有一种轻微的泥土气味和氢氧化钙的苦涩碱味。英文中的“lime”指的是碱性的石灰, 而与酸性的青柠并无关系。 石灰水是通过将氢氧化钙在纯水中搅拌溶解，再滤去多余未溶解的Ca(OH)₂。当多余的氢氧化钙被加入到石灰水中时，会产生悬浮的氢氧化钙颗粒，使它呈现出乳白色的面貌，在这种情况下它通常被称为石灰乳。石灰乳和饱和石灰水的pH约为12.3。

Limewater is the common name for a diluted solution of calcium hydroxide. Calcium hydroxide, Ca(OH)₂, is sparsely soluble in water (1.5 g/L at 25 °C). Pure limewater is clear and colourless, with a slight earthy smell and an alkaline bitter taste of calcium hydroxide. The term lime refers to the alkaline mineral, and is unrelated to the acidic fruit.