Answer:
The sand is much warmer than the water because water has a higher specific heat, or it takes more energy to change the temperature of water. Since they are absorbing energy from the same place, the sun, the sand will get warmer faster because it takes less energy to change the temperature.
Another reason could be because the water is constantly mixing with the water below it which is not exposed to the sun and because of this the water remains at a lower temperatre. The sand however has the same part exposed to the sun unless an external force, a foot, umbrella, wind, etc comes to move it. So it is able to absorb the sun for longer than the water.