I have a Brinkman Water Smoker, and use it for turkey all the time.
I have found that splitting the turkey in halves will give a better
product. I smoke mine for 10-12 hours, using charcoal or hardwood,
and lots of chips or shavings, like hickory, or apple. Soak the
chips, etc, and place them in a "tray" made of foil on the coals.
Be sure to stir the coals and add new chips and coals as needed,
every few hours.
Instead of plain water, I usually make "potpourri" for the water
pan. In a large pan, bring water to a boil, while adding such
items as cinnamon sticks, fresh fruit such as apples, pears, oranges,
limes, etc. I also add a few bay leaves and cloves. The result
is a very "fruity & spicy" steam, which permeates the meat.
As for the bird itself, I use a dry rub at times, sometimes nothing
at all. About halfway through the cooking process, switch the top
rack and the bottom rack to even out the cooking.
I got better heat from mine after I drilled a series of holes in
the fire pan, to let the ashes out, and improve the air draw.