And things get dramatically worse on 4o if you add a second superfluous jug:

    To measure exactly 6 liters of water using a 16-liter jug, a 12-liter jug, and a 6-liter jug, follow these steps:
    Step-by-Step Solution:

        Fill the 12-liter jug completely (it now holds 12 liters).
        Pour water from the 12-liter jug into the 16-liter jug. The 16-liter jug now contains 12 liters, and the 12-liter jug is empty.
        Fill the 12-liter jug completely again (it now holds 12 liters).
        Pour water from the 12-liter jug into the 16-liter jug until the 16-liter jug is full. Since the 16-liter jug already has 12 liters, it can only take 4 more liters. This leaves 8 liters in the 12-liter jug.
        Empty the 16-liter jug completely.
        Pour the remaining 8 liters from the 12-liter jug into the 16-liter jug.
        Fill the 12-liter jug completely again (it now holds 12 liters).
        Pour water from the 12-liter jug into the 16-liter jug until the 16-liter jug contains exactly 16 liters. Since the 16-liter jug already has 8 liters, it can only take 8 more liters, leaving 4 liters in the 12-liter jug.
        Pour the 4 liters from the 12-liter jug into the empty 6-liter jug. The 6-liter jug now contains 4 liters.
        Fill the 12-liter jug completely again (it now holds 12 liters).
        Pour water from the 12-liter jug into the 6-liter jug until the 6-liter jug is full. Since the 6-liter jug already has 4 liters, it can only take 2 more liters. This leaves 10 liters in the 12-liter jug.
        Empty the 6-liter jug completely.
        Pour the remaining 10 liters from the 12-liter jug into the 6-liter jug.

    Now, the 6-liter jug contains exactly 6 liters of water.