For the simple syrup: In small saucepan, combine the water and sugar together. Bring to a boil over medium heat, stirring constantly, until sugar is completely dissolved. Reduce heat to medium-low and boil gently for 3-4 minutes, stirring occasionally. Remove from heat and cool to room temperature (apx. 30-40 minutes). Add the lemon juice and lemon rind. Let mixture steep for at least an hour (or up to three hours) to allow the flavors to blend. Strain mixture twice through a fine mesh sieve to remove the lemon pulp and rind. Discard the pulp and rind.

For the rhubarb and peach juice: Combine the rhubarb, peaches (and their stones), and water in a large pot. Cover and bring to a boil then reduce heat to medium-low and cook for approximately 8-10 minutes, or until rhubarb and peaches are completely softened and mushy.

Place a large sieve over a big heatproof bowl or large measuring cup. Line the sieve with 3-4 layers of damp cheesecloth.

Remove the rhubarb and peach mixture from the heat and discard the peach stones. Use a potato masher to mash down the mixture. Pour mixture into the sieve, letting the juice drip through. It may be necessary to use the back of a large spoon to very gently press the pulp in order to extract all the juice out of the rhubarb and peaches. This should yield about 6½ cups, depending on the age and juiciness of the rhubarb. If it is slightly less than 6½ cups, up to ½ cup water may be added to bring the amount to 6½ cups.

To assemble: In large jug or bottle, combine the strained fruit juice with the simple syrup and lemon juice mixture. Stir well. Chill.

To serve: Stir the chilled lemonade and pour into glasses. Add ice cubes and garnish with a lemon slice, if desired.

Lemonade will keep, covered, in the refrigerator for 3-4 days. Freezes well.