Add Water to WSM 18.5inch/47cm

When cooking low and slow on 18.5inch/47cm wsm for approx 8-10 hrs how often do you need to add water. Thanks

Never (for me). Rock solid at 225-240.

edit-->I should add, that was when I used water. Exclusively foiled clay saucer for the last 2-3 yr now.

Full water pan would last at least 8 hrs for me.

I have a 22.5" WSM and I foil the water pan. I fill mine just about 1/2 way and it lasts the entire cook.

After closing the vents so the coals go cold I scoop out the ashes and transfer them to the water pan. The water soaks up most (to all) of the water and creates a kind of mud-like substance. Then I fold in the foil (bringing the seam ends together first) before folding it into a nice "pillow" that slips neatly into an empty briquette bag for the trash.