Let the total number of deer in the herd be \( x \).
According to the problem:
- Half of the herd is grazing in the field, which is \( \frac{x}{2} \).
- The remaining deer are \( x - \frac{x}{2} = \frac{x}{2} \).
- Of these remaining deer, three-fourths are playing nearby. So, the number of deer playing is \( \frac{3}{4} \times \frac{x}{2} = \frac{3x}{8} \).
- The rest, which are drinking water from the pond, are \( \frac{x}{2} - \frac{3x}{8} \).
Now, let's simplify \( \frac{x}{2} - \frac{3x}{8} \):
- First, convert \( \frac{x}{2} \) to eighths: \( \frac{x}{2} = \frac{4x}{8} \).
- Now, we have: \[ \frac{4x}{8} - \frac{3x}{8} = \frac{x}{8} \]
According to the problem, the number of deer drinking water is 9: \[ \frac{x}{8} = 9 \]
Now, solve for \( x \): \[ x = 9 \times 8 = 72 \]
Thus, the total number of deer in the herd is \( \boxed{72} \).