My chemistry is not all it should be, but here is what I remember from chemistry class. One of the easiest is to light a candle. This obviously produces other things than just water, including smoke, carbon, light, heat, but it also produces a small amount of water vapor.
Candle wax is made of molecules made primarily of chains of carbon and hydrogen.
When heated, the wax melts, is absorbed into the wick and burns. During the burning process, the carbon and hydrogen are separated and the hydrogen combines with oxygen to form water vapor. When hydrogen is burned in the presence of oxygen, the hydrogen and oxygen combine to form H20, or water. So, cars make water when they burn gasoline, and we make water when we digest food. There are other chemical reactions that also produce water, but combustion and respiration are the most common.