system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do water temperatures feel different before, during, and after swimming?

You get in the pool and the water feels cold. Then you get used to it and it no longer feels cold. Then it’s time to get out of the pool and it feels warmer in the water than it does outside. I don’t understand.
gpt
Your body can only sense the difference in temperature, not the actual temperature like a thermometer.

You can try this out by having 3 bowls containing warm, room temperature, and cold water. Put one hand in the warm water and your other in the cold water for about a minute. Then move your hands into the room temperature water.

The hand in warm water will feel cold while the hand cold water will feel warm despite the fact that your hands are in water of the same temperature.

The same happens at the pool. Your skin temperature is normally higher than the water temperature. When you first dip in, your skin feels the huge temperature difference and it feels cold!

But over time, the skin's temperature adjusts to the water's temperature and you don't feel any difference. You still have to move around and generate more heat from playing and swimming. Remaining stationary in cool water can lead to hypothermia as water can remove heat faster than air.

Getting out of the water feels cold because of evaporative cooling, the same effect where sweat cools you down. The pool water on your skin starts to vaporize and carry heat with it, cooling the skin. If you get back in the water, it stops this effect, making you feel warmer. Drying yourself off also stops the evaporative cooling and can also make you feel warm despite no changes in air temperature.