Which of the following is not a disadvantage of using hard water?

Explanation

To determine which of the following is not a disadvantage of using hard water, we need to analyze the options provided. Hard water is characterized by the presence of dissolved minerals, primarily calcium and magnesium ions, which can lead to various disadvantages in different applications.

### Step-by-Step Solution:

1. **Identify the Disadvantages of Hard Water**:
- Hard water can lead to the formation of scale in boilers and cooking utensils. This scale can reduce the efficiency of heating systems and make cleaning difficult.
- Hard water can also cause issues in laundry, as it can react with soap to form scum, reducing the effectiveness of cleaning.

2. **Analyze the Options**:
- **Option A**: Production of steam in boilers. This is a disadvantage because hard water can lead to scale formation in boilers, which can reduce efficiency and increase maintenance costs.
- **Option B**: Formation of scales in cooking utensils. This is also a disadvantage, as it leads to unsightly deposits and can affect the cooking process.
- **Option C**: Ion exchangers. This is where hard water can actually be beneficial. In ion exchange processes, hard water can be treated to remove calcium and magnesium ions, effectively softening the water. This means that using hard water in ion exchangers does not present a disadvantage.

3. **Conclusion**:
- Since options A and B are disadvantages of using hard water, and option C is not a disadvantage, we conclude that the correct answer is **Option C**.

### Final Answer:
**Option C: Ion exchangers** is not a disadvantage of using hard water.