You can make fire quite easily using water!

The basic idea is to take a piece of plastic wrap (Saran or otherwise) and form it into a “pocket”, i.e. bring the four corners together.

The pocket is then filled with water.

The corners are then grouped together and twisted until the whole assembly resembles a sphere. This creates a makeshift lens.

It was pretty easy to start a fire using cedar bark tinder.

Using tinder fungus would of course made things even easier.

Yap. The old-fashioned lens method, without the store-bought lens.

Pictures and details here