If the temperature in the room is 16 °, then we are not cold, but if we enter the water

If the temperature in the room is 16 °, then we are not cold, but if we enter the water with a temperature of 18 °, then we feel rather strong cold. why?

This is because the thermal conductivity of air is about 27 times less than the thermal conductivity of water under normal conditions. Accordingly, when we are in a room, per unit of time, our body loses less heat than when we immerse ourselves in water, which removes heat from us much more strongly upon contact with the skin.