Wash and trim the rhubarb into 1cm (less than ½ in) slices. To poach the rhubarb, combine the water and the sugar in a saucepan, stir, and bring to a boil. Then add the sliced rhubarb, cover, bring to the boil, and simmer for exactly 1 minute. Turn off the heat and leave the rhubarb in the covered saucepan until it is almost cool. Transfer to a bowl to finish cooling.