Combine the chopped rhubarb, water and sugar in a sauce pan and cook over medium heat while continuing to stir, letting the rhubarb break down.

Bring to a boil, then reduce heat and let simmer for 10 minutes.

Remove from heat and let cool. Once cooled, strain through a fine meshed strainer into a mason jar.

Add in the vinegar and mix well. Keep in the fridge until ready to use in a cocktail.