Put the sugar and cold water in a
saucepan and heat gently, stirring, until the sugar has dissolved.
Bring to the boil rapidly until the mixture is a rich brown color (but
not burnt!). Remove from the heat and pour in the warm water (take
care as it may splutter). Return to the heat and stir until the
caramel melts, then boil rapidly until syrupy. Leave to cool. If the
mixture is too thick when cooled, stir in a little warm water.