Cut cauliflower into bite-sized chunks and cut potatoes into 1-inch cubes.
In a large heavy pot sauté turmeric, ginger, cayenne pepper, cumin and coriander in the vegetable oil for 3 minutes. Add tomatoes, potatoes, cauliflower, and salt. Stir to mix. Add the water. Bring to a boil.
Cover and simmer over low heat for 30 minutes or until vegetables are tender. Sprinkle with garam masala. Serve with rice.