Cook bacon in a large skillet over medium-high heat until evenly browned, about 10 minutes. Drain all but about 2 tablespoons bacon drippings from skillet. Cook and stir onion with bacon in reserved drippings until onion is translucent, 5 to 10 minutes. Add garlic; cook and stir until fragrant, 2 minutes.

Pour Alfredo sauce into onion-bacon mixture; rinse jar with the water and pour into skillet. Stir sauce with a wooden spoon, thoroughly scraping any brown bits of food from bottom of the skillet. Bring sauce to a simmer; add tomatoes. Simmer sauce until flavors blend, about 5 minutes.