A sample of water which does not produce lather with soap readily
is called heavy water.

Explanation

To solve the question, we need to clarify the terms used in the statement and understand the properties of different types of water.

### Step-by-Step Solution:

1. **Understanding the Statement**: The statement claims that a sample of water which does not produce lather with soap readily is called heavy water.

2. **Identifying Types of Water**: Water can be classified into two main types based on its ability to form lather with soap:
- **Soft Water**: This type of water readily produces lather with soap. It contains fewer dissolved salts.
- **Hard Water**: This type of water does not produce lather readily with soap. It contains higher concentrations of dissolved minerals, particularly calcium and magnesium salts.

3. **Correcting the Statement**: The statement incorrectly uses the term "heavy water." The correct term for water that does not produce lather with soap is "hard water."

4. **Defining Heavy Water**: Heavy water is a specific type of water that contains a higher proportion of the isotope deuterium (D) instead of the more common hydrogen isotope (H). Its chemical formula is D2O, and it is not related to the lathering properties of water.

5. **Conclusion**: Therefore, the statement is false. The correct classification for water that does not produce lather with soap is hard water, not heavy water.

### Final Answer:
The statement is false. A sample of water that does not produce lather with soap readily is called hard water, not heavy water.