Question

The tap water found in many areas of the United States leaves white deposits when it evaporates. Is this tap water a mixture or a compound? Explain.

Short answer

Tap water is a mixture as it contains water with some dissolved chemicals such as calcium or magnesium carbonates and sometimes fluorides.

Step-by-step solution

Mixture 

Mixtures are made by mixing two different components physically not in a fixed ratio.

Why tap water is a mixture 

Given that white substance is deposited on evaporation of water it shows that the tap water has calcium as a dissolved mineral in it.

So we can say that tap water is a mixture as it contains water with some dissolved chemicals such as calcium or magnesium carbonates and sometimes fluorides.