Cook bacon in a large pot over medium-high heat, stirring occasionally, until crisped and browned, about 10 minutes. Transfer bacon with a slotted spoon to a paper towel-lined plate. Leave drippings in the pot.
Place potatoes and carrots into the pot and season with salt and pepper; cook in bacon drippings, stirring frequently, for 5 minutes.
Pour clam juice into the pot, add enough water to just cover potatoes, and bring to a boil. Reduce the heat to medium-low, cover, and simmer until potatoes are just tender, 10 to 15 minutes.
Add leek soup mix and gently stir until no lumps remain. Stir in clams, half-and-half, and reserved bacon. Cook and stir until chowder returns to a simmer and thickens, about 10 minutes more.
