Evaporating water is essential to helping your body cool down. Imgorthand/E+ via Getty ImagesCurious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.Why is water wet? – Philip S., age 12, Northville, MichiganSpring 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 atmospheric scientist, 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 seeImagine 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 called adhesion.One important reason why water molecules are so attracted to other molecules is that they’re polar. Like a microscopic magnet, one end of the molecule carries a small negative charge, while the other end carries a small positive charge. Water, also known as H2O, has a slightly negative charge surrounding its oxygen atom and a slightly positive charge around its hydrogen atoms. Riccardo Rovinetti/Wikimedia Commons, CC BY-SA 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 very strong cohesion. As a result, mercury does not easily stick to other surfaces.The cool feeling of being wet comes from evaporation. Liquids need energy to change into gas because they must overcome the forces holding molecules together before they can float away. They take this energy from their surroundings in the form of heat. As temperature increases, the adhesion between molecules decreases. OpenStax, CC BY-SA 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 sweat evaporates, it removes heat from your body and cools you down.Wet you cannot seeSometimes you can feel damp even when you don’t see any water. This is related to the amount of water vapor in the air, 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 completely full of water vapor, 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. Warm air can hold more water vapor, while cold air can hold less. As temperature increases, water molecules gain more energy 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. Shady, cool areas can feel wet even when you don’t see water around. Ketut Agus Suardika/iStock via Getty Images Plus A lot of water, but not wetBecause 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 burning process produces water vapor. 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 relative humidity 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 wildfires release large amounts of water vapor. Fire is the last thing most people associate with being wet.Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.Yunyao Li does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.