Wash the rhubarb and cut it in pieces. Put into a pan with the water and simmer until tender. Sieve and return to the pan. Bring to the boil, stir in the sugar, and cook over low heat, stirring well until the sugar has dissolved. Cook and stir until the mixture is thick and creamy. Add a little red food colouring as the colour of this mixture will be pale brown. Pour into hot jars and cover.