In medium saucepan, heat oil over medium-low heat. Stir in onion and garlic and cook until onion is soft and translucent. Stir in tomato sauce, water, salt and pepper. Cover and simmer gently for 10 minutes. Stir in cream, cover and set aside.
Cook spaghetti as directed on box. When pasta is done, take out 1/2 cup cooking water and reserve.
Drain pasta and return to cooking pot. Add basil and some reserved cooking water as needed. Taste and adjust seasoning. Serve immediately with cheese.