Which type of water has the highest value of water potential?

Options

A. Salt water
B. Pure water
C. Tap water
D. Boiled water

Answer

To determine which type of water has the highest value of water potential, we need to understand the concept of water potential and the factors that influence it.

### Step-by-Step Solution:

1. **Understanding Water Potential**:
- Water potential (Ψ) is a measure of the potential energy of water in a system and is influenced by two main components: solute potential (Ψs) and pressure potential (Ψp).
- The formula for water potential is given by:
\[ Ψ = Ψp + Ψs \]

2. **Analyzing Solute Potential**:
- Solute potential (Ψs) is always negative or zero because it represents the effect of solute concentration on the potential energy of water.
- Pure water has a solute potential of zero (Ψs = 0), as there are no solute particles present.

3. **Analyzing Pressure Potential**:
- Pressure potential (Ψp) can be positive or zero. It is the pressure exerted by the water in a system.
- In open systems, like pure water, the pressure potential is also zero (Ψp = 0).

4. **Calculating Water Potential for Different Types of Water**:
- **Pure Water**:
- Ψs = 0, Ψp = 0
- Therefore, Ψ = 0 + 0 = 0
- **Tap Water**:
- Typically has some solute, resulting in a negative solute potential (e.g., Ψs = -15 MPa).
- Thus, Ψ = Ψp (which may be positive) + Ψs = positive value + negative value (resulting in a negative water potential).
- **Boiled Water**:
- Contains fewer solutes than tap water, but still has some solute, leading to a less negative value (e.g., Ψs = -5 MPa).
- Thus, Ψ = Ψp + Ψs = positive value + (-5 MPa) = still negative but less than tap water.

5. **Conclusion**:
- Among the types of water discussed, pure water has the highest water potential, which is 0 MPa. All other types of water have negative water potentials due to the presence of solutes.

### Final Answer:
**Pure water has the highest value of water potential, which is 0 MPa.**