Adjust oven rack to upper-middle position and heat oven to 500 degrees.
Toss Brussels sprouts, 3 Tablespoons olive oil, water, salt and pepper in large bowl until sprouts are well coated. Transfer sprouts to rimmed baking sheet and arrange so cut sides are facing down.
Cover sheet tightly with foil and roast for 10 minutes.
Remove foil and continue to cook until Brussels sprouts are well browned and tender, about 10-12 minutes.
While sprouts are roasting, cook bacon in a 10" skillet until crisp, about 7-10 minutes.
Remove bacon and transfer to a plate lined with paper towels. Reserve 1 Tablespoon bacon fat. When cool enough to handle, finely chop bacon.
In a skillet, or in the oven, toast pecans until they are golden and fragrant. When cool, chop.
Toss cooked Brussels sprouts with 1 Tablespoon reserved bacon fat, 2 Tablespoon olive oil, chopped bacon, and chopped pecans. Season to taste.