1. Peel, core, and dice the tomatoes. (To peel the tomatoes, immerse them in boiling water for 20 to 30 seconds and then dip them in cool water. The peels will slip off.)
2. In a large saucepan, heat the olive oil over medium heat and saute the garlic and onion until tender, 4 to 5 minutes. Add the tomatoes, water, basil leaves, parsley, salt, and pepper.
3. Bring to a boil and then reduce the heat, simmering uncovered for 45 minutes and stirring occasionally to make sure the tomatoes are well mixed.
4. If you prefer a smooth sauce, allow the sauce to cool and then blend in a food processor. Refrigerate the leftover sauce for up to 5 days or freeze until needed.