Where does the water slowly go?

When the sun heats up water, its tiny particles gain enough energy to break free from the liquid and float into the air as invisible water vapor, a process called evaporation. Over a hot day, enough of these particles escape that the water level in the glass slowly drops even though nothing visibly spills.

Water can't sink into a glass since glass doesn't soak up liquid the way a sponge or paper towel does, and water definitely can't turn into sand, since sand is a completely different solid material made of tiny rock and mineral grains.

That evaporated water doesn't just disappear forever — it rises, cools, and clumps into clouds, eventually falling back down as rain in an endless loop called the water cycle.