Using 2 subintervals:
Total interval = 0 to 4, so
\[
h = \frac{4 - 0}{2} = 2
\]
Simpson's 1/3 rule:
\[
I = \frac{h}{3}\left[f(x_0) + 4f(x_1) + f(x_2)\right]
\]
Values:
\(x_0 = 0,\; x_1 = 2,\; x_2 = 4\)
\[
f(0)=\sqrt{0}=0, f(2)=\sqrt{2}=1.414, f(4)=\sqrt{4}=2
\]
Thus,
\[
I = \frac{2}{3}(0 + 4(1.414) + 2)
\]
\[
I = \frac{2}{3}(7.656) = 5.104
\]
Rounded to 3 decimals:
\[
\boxed{5.104}
\]