```
Pressure (psi) = (Depth in feet) x (Density of water in psi per foot)
```
The density of water is approximately 0.445 psi per foot. So, the water pressure at a depth of 300 feet would be:
```
Pressure (psi) = (300 feet) x (0.445 psi per foot) = 133.5 psi
```
Therefore, the water pressure at a depth of 300 feet is approximately 133.5 psi.
