The answer is perfect when cotton6894 and laohuzhou88 are combined.
The specific heat of water is higher than that of stone and its thermal conductivity is lower than that of stone. Therefore, the temperature is the same and the volume is the same (the density of the stone is the same). about 4, which is equivalent to the heat capacity of water of the same volume), and the water falls slowly.
If you want the water temperature to drop slowly, you can keep it warm and reduce the heat dissipation area. . . . . .
Adding oil may slow the cooling rate. Most of the oil will float on water, which not only retains heat but also reduces the heat dissipation area.