Bring water, kielbasa, and 2 whole cloves garlic in a large pot to a boil over high heat, then reduce heat to medium and simmer for 30 minutes. Remove sausage; pour cooking liquid into a separate bowl. Cut sausage into bite-sized pieces. Discard garlic.

Melt butter over medium heat in the same pot. Add leeks, onion, and minced garlic; cook and stir until vegetables are tender, about 5 minutes.

Transfer vegetables and about 1/2 cup reserved cooking water to a blender, filling halfway. Cover and hold lid down with a potholder; pulse a few times before leaving on to blend until smooth, adding more water as needed. Pour back into original pot. Repeat with any remaining vegetables.

Add remaining cooking water and bay leaves to vegetable purée; bring to a simmer over medium heat. Remove and discard bay leaves.

Whisk sour cream and flour together in a bowl until smooth; gradually whisk into soup until thickened. Stir in dill and vinegar, then season with salt and pepper.