Water containing dissolved common salt may be regarded as hard water.

Answer

**Step-by-Step Solution:**

1. **Understanding Hard Water**: Hard water is defined as water that contains high concentrations of dissolved minerals, specifically salts of calcium (Ca²⁺) and magnesium (Mg²⁺). These minerals can be present in the form of carbonates, sulfates, or chlorides.

2. **Identifying Common Salt**: Common salt, chemically known as sodium chloride (NaCl), is a compound that dissolves in water but does not contribute to the hardness of water. It does not contain calcium or magnesium ions.

3. **Types of Hardness**:
- **Temporary Hardness**: This type of hardness is primarily caused by the presence of bicarbonates (hydrogen carbonates) of calcium and magnesium. For example, magnesium bicarbonate (Mg(HCO₃)₂) contributes to temporary hardness.
- **Permanent Hardness**: This type of hardness is due to the presence of chlorides and sulfates of calcium and magnesium. Examples include magnesium chloride (MgCl₂) and magnesium sulfate (MgSO₄).

4. **Conclusion**: Since common salt (NaCl) does not contain calcium or magnesium, it does not contribute to the hardness of water. Therefore, water containing dissolved common salt cannot be regarded as hard water.

5. **Final Answer**: No, water containing dissolved common salt may not be regarded as hard water.

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