Why is water wet?
By: , Assistant Professor of Earth and Environmental Sciences, , for 
Spring is often a rainy season. If you get caught in a downpour without an umbrella, you will quickly learn what it means to be wet. But what is it about water that makes it wet?
I am an , and water is a fundamental part of the atmosphere. I study storms and wildfires, both of which are closely connected to water.
Why water is wet has to do with how water molecules interact with each other and the things around them.
Wet you can see
Imagine you accidentally spill water on your clothes one day. You will notice two things: First, the water spreads out on the cloth, and the wet part sticks to your body more than the dry part does; and second, the wet area feels cool.
Wet clothes stick to your body and water spreads across the fabric because water molecules are strongly attracted to other molecules, a chemical property .
One important reason why water molecules are so attracted to other molecules is that . Like a microscopic magnet, one end of the molecule carries a small negative charge, while the other end carries a small positive charge.
Many everyday materials, such as glass, skin and clothing, are also polar. When water touches these surfaces, the electric charges on those materials attract the water molecules and hold them in place. This strong attraction also helps water spread out over surfaces. Whether something feels “wet” to you has to do with how good a liquid is at staying in contact with a surface. Water feels wet because its molecules stick tightly to each other and to your skin.
Compared to water, mercury has much weaker attraction to surfaces. Mercury’s molecules are much more attracted to each other, meaning they have . As a result, mercury does not easily stick to other surfaces.
The cool feeling of being wet comes from evaporation. because they must overcome the before they can float away. They take this energy from their surroundings in the form of heat.
When you step out of a pool and the water on your swimsuit evaporates, you might feel cold because it’s taking away heat from your body. Wet things often feel cool because evaporation takes heat away from the skin. Sometimes something that feels cool can trick you into thinking it’s also wet, even if no liquid is actually present.
Evaporative cooling is very useful in daily life, and other liquids can also do it. For example, when you clean a wound with an alcohol wipe, it also feels cool. Like water, alcohol evaporates and carries heat away from your body. Similarly, when , it removes heat from your body and cools you down.
Wet you cannot see
Sometimes you can feel damp even when you don’t see any water. This is related to the amount of , also called humidity.
Air can hold only a limited amount of water vapor. When there is already a lot of water vapor in the air, evaporation slows down. This makes it harder for sweat on your skin to evaporate, so you feel sticky and wet.
When air becomes , the vapor starts to condense and turn back into liquid water to form dew or fog.
How much water vapor air can hold depends on temperature. , while cold air can hold less. As temperature increases, water molecules and can more easily escape their attraction to each other and become a vapor.
This is why dark or shady places often feel damp. These areas get less sunlight, stay cooler and cannot hold much water vapor. As a result, water does not evaporate easily and the area stays wet.
A lot of water, but not wet
Because the air’s ability to hold water depends on temperature, sometimes the air can contain a lot of water vapor but you don’t feel wet.
For example, when you are near a fire, the . However, because the temperature is also higher, the air can hold more water vapor. This speeds up evaporation. If there are wet clothes nearby, they may actually dry more quickly.
In weather forecasts, scientists use to describe how humid the air feels, rather than the actual amount of water vapor in the air.
Because hot air can hold so much moisture that relative humidity stays low, people are often surprised when I tell them that . Fire is the last thing most people associate with being wet.
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