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