What type of water forms scum with soap?

Explanation

To determine what type of water forms scum with soap, we can follow these steps:

### Step 1: Understand the Composition of Water
Water can be classified into two main types: hard water and soft water. The difference lies in the presence of certain minerals.

### Step 2: Identify Hard Water
Hard water contains high concentrations of dissolved minerals, specifically calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions can come from various sources, such as the dissolution of limestone or other mineral deposits in the water supply.

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