Preheat the oven to 350 degrees F.
Grease and flour 12 muffin cups.
Combine the water, raisins, dates and prunes in a saucepan over medium high heat.
Boil for about 5 minutes (until the water is absorbed), then remove from heat, add the butter pieces and stir until the butter is melted.
Transfer to a large bowl and let cool.
Beat in the eggs and vanilla. Stir together the flour, baking powder, baking soda and salt.
Mix in the walnuts (if using) and blend into the fruit mixture.
Spoon the mixture into the muffin cups (2/3 to 3/4 full).
Bake in the oven for about 15-20 minutes (or until an inserted toothpick comes out clean