In a large pot, cook the bacon over medium-high heat until crisp and browned, 4 to 6 minutes. With a slotted spoon, transfer the bacon to paper towels to drain.
Add the white green onions and potatoes to the pot; cook, stirring, until the green onions are softened, 1 to 3 minutes. Add the flour and cook, stirring, 1 minute. Add milk, Old Bay, thyme and the water. Bring to a boil, then reduce to a simmer, and cook, stirring occasionally, until potatoes are tender, 10 to 12 minutes. Add the corn, shrimp and green onions. Cook until the shrimp are just opaque, 2 to 3 minutes. Season with salt and pepper. Serve immediately topped with bacon and crackers.