Density of water is highest at $4°\text{C}$. This is due to

Molecules exist in 3 types ($H_{2}O$),${\left(H_{2}O\right)}_2$ and ${\left(H_{2}O\right)}_3$.  The number of these molecules change with temperatures.  At 4°C, the number of ${\left(H_{2}O\right)}_3$ and ${\left(H_{2}O\right)}_2$ molecule sis high, so volume occupied is minimum.