* Tap water is not pure water: It contains dissolved minerals and salts, such as calcium, magnesium, and chloride. These minerals are what make up the white residue.
* Evaporation separates the water: When water evaporates, it leaves behind the dissolved minerals. These minerals are not chemically combined, so they remain as a mixture.
* The composition varies: The exact composition of the residue will depend on the source of the water and the types of minerals dissolved in it.
Therefore, the white substance is a mixture of different minerals and salts, not a pure substance.
