noun
limewater
A clear, saturated solution of calcium hydroxide used in chemistry, cooking, and as a test for carbon dioxide.
石灰水に二酸化炭素を通すと白く濁る。
When carbon dioxide is passed through limewater, it turns milky.
石灰 (lime) is the solid calcium oxide or hydroxide; 石灰水 is specifically the aqueous solution.
Compound of 石灰 (せっかい, 'lime') and 水 (すい, 'water').