To answer this question, we need the height equation of the rock above the water. Since the equation wasn't provided in your question, I'll generalize the process of finding the time it takes for the rock to hit the water.
The rock will hit the water when its height above the water is 0. Therefore, you would set the height equation equal to 0 and solve for \( t \).
For example, if the height function \( h(t) \) is in a standard quadratic form such as
\[ h(t) = -16t^2 + vt + h_0 \]
where \( v \) is the initial velocity and \( h_0 \) is the initial height, you'd set:
\[ -16t^2 + vt + h_0 = 0 \]
You would then use the quadratic formula:
\[ t = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]
where \( a = -16 \), \( b = v \), and \( c = h_0 \).
If you have the specific height function, please provide it so that I can assist you in finding the specific time it takes for the rock to hit the water.