One of the easiest things to make in Little Alchemy is water. To do this, you simply need to drag the air element onto the fire element. This will create steam, which can then be combined with the earth element to create water.
Other easy combinations include: earth + fire = lava; air + earth = dust; and fire + water = energy. These are just a few of the many possible combinations that can be made in Little Alchemy. With a bit of experimentation, you'll be able to discover even more!