Cut the potatoes into 20mm cubes. Heat the oil in a large frying pan and fry the sausage until brown all over. Remove the sausage, slice in 25mm lengths and set aside.
Add the the onion and chili peppers to the pan and stir fry until the edges of the onion pieces are turning brown. Remove and set aside.
Add the cubed potatoes to the pan with a little more oil if necessary and stir fry until brown all over.
Return the sausage, onions and chilis to the pan and add the water, tomatoes, salt and pepper and bring to the boil. Cover tightly and simmer for about 20 minutes, stirring occasionally and adding a little more water if necessary.