1. In a large saucepan over medium heat, saute the bacon until it is crisp and all bacon fat has been rendered. Remove the bacon from the pan, dice and set aside.
2. In the same saucepan, add 2 tablespoons butter to the bacon drippings. When butter has melted, make the roux by adding flour and cooking on low heat for 3 to 4 minutes. Remove roux from pot and set aside.
3. Add remaining butter to pot and saute the onions and celery over low heat to soften. Return roux to pot, and add the water and clam juice. Raise the heat to high and cook, stirring frequently for 6 to 8 minutes, until thickened. Add clams, bacon, potatoes, seasonings, cream and half-and-half. Simmer about 10 minutes.