system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does water feel colder than air if they're the same temperature?

For example, when water is 20°C, it feels colder than 20°C air.
gpt
Water is able to hold more thermal energy than air. It's *also* more thermally conductive, so it allows heat to transfer faster.

So in both of your examples, your skin is leaking heat into the surrounding environment. But the water touching your body takes far more energy to heat the same volume. And it can take that energy faster than the air can. This is why very cold water can kill you very quickly but a non-windy day at the same temperature is little more than uncomfortable unless you spend considerable time in it.