Place water, tomatoes, and olive oil in a blender or food processor; blend until smooth. Transfer tomato mixture into a large pot.
Stir sugar, garlic salt, and vinegar into tomato mixture and bring to a boil. Reduce heat to medium-low and simmer until thickened, stirring occasionally, about 1 to 2 hours.
Pour tomato mixture into a clean blender or food processor no more than half full. Cover and hold lid down; pulse a few times before leaving on to blend until very smooth. Repeat with any remaining tomato mixture.