In a soup pot, cook the bacon until crisp; remove and reserve. To the bacon fat, add the leeks and cook until tender, about 4 minutes. Add the potatoes and water. Bring up to a boil, reduce the heat to a simmer and add half-and-half. Cook until the potatoes are tender, about 20 minutes. Add the clams and bacon and continue cooking for 3 minutes. Season with salt and white pepper. Garnish with shaved green onions and Creole seasoning, if desired.