To find the square root of \( 0.0009 \), write it as:
\[ \sqrt{0.0009} = \sqrt{\frac{9}{10000}} \]
\[ = \frac{\sqrt{9}}{\sqrt{10000}} \]
\[ = \frac{3}{100} = 0.03 \]
Thus, the square root of 0.0009 is \( 0.03 \).