(optional) Cook the fruit in a saucepan with the water or fruit juice until the fruit is soft.
In a blender or food processor, blend the fruit and liquid well. Add the liquid gradually, as the fruit should be easy to spread but not too watery.
Line a cookie sheet or sheet pan with parchment paper then spread the fruit over the pan evenly. Give the pan a few shakes from side to side to even out the surface of the fruit. Set your oven to the lowest setting (usually about 150 degrees.) Place the pan in the oven for 8-12 hours (I usually put my fruit leather in when I go to bed, and it's usually done by noon the next day, depending on the fruit.)
You will know your fruit leather is done when it is shiny on top but not sticky, and when it peels away from the paper easily.