Clean and chop the tomatoes. You can skin them if you like. It adds flavour to the jam. Add water in a vessel and heat it on a medium to high flame. Add the cleaned and chopped tomato. Cover it and cook till the tomato gets soft and smash it well with a wooden spoon. Add the lemon juice and bring to the boil. Then add the sugar and stir till dissolved. Continue cooking until the jam reaches a desired texture by stirring continuously. When it becomes a thick solution, remove from fire and pour into a bottle.