Heat oil in a Dutch oven. Add onion and cook until softened. Add beef to the pot and brown well. Stir in tomato sauce and paprika, and enough water to cover meat well, about 4-5 cups. Bring to a boil, lower heat and cover, and simmer for 1-1/2 hours. Add potatoes to pot, making sure they are covered by the liquid, and cook for another 45 minutes, until potatoes are tender.