To divide \( \frac{1}{2} \) gallon of water equally among 5 plants, we need to perform the division of \( \frac{1}{2} \) by 5.
This can be expressed as: \[ \frac{1}{2} \div 5 \]
Dividing by a number is the same as multiplying by its reciprocal. The reciprocal of 5 is \( \frac{1}{5} \). Therefore: \[ \frac{1}{2} \div 5 = \frac{1}{2} \times \frac{1}{5} \]
Now, multiply the fractions: \[ \frac{1 \times 1}{2 \times 5} = \frac{1}{10} \]
Thus, each plant receives: \[ \frac{1}{10} \text{ gallon of water.} \]
So the answer is: \[ \frac{1}{10} \text{ gal.} \]