Combine the chopped rhubarb, water and sugar in a pot. Bring to a boil and then reduce the heat to a low simmer. Cover and let simmer for 15 minutes. Turn off the heat and leat sit for another 15 minutes if desired. Strain through a fine mesh strainer, pressing the pulp to drain as much of the syrup as you can. Let cool and then store in the fridge until needed. This will make approximately 3 cups of syrups, enough for about 15 cocktails.