2 liters of water per day is not excessive. That's about the amount recommended for most folks (eight 8 oz. glasses). What may be causing your nighttime bathroom trips may be all the other stuff you drink after 6 when you are done with your water. If you were going to cut back on anything, I'd suggest cutting back there first.
There are also times when you are losing weight quickly that you may notice an increase in urination. Your body has to get rid of the byproducts of fat metabolism and they do it via the kidneys, so deliberately restricting fluids could actually slow you down and put more stress on your body.