Heat the water in a saucepan. Slowly bring the tomato paste, curry powder, paprika powder, sugar, sambal oelek, soy sauce and salt to the boil while stirring. Remove the pot from the oven. Stir in tomato ketchup and vinegar and bring to the boil again.
Tip: I recommend buying tomato paste of a higher quality, so the sauce will be a bit fruity, since cheap tomato paste tastes bitter. The spiciness can be adjusted with the sambal oelek and the consistency with the water.