The water is merely used as a heat sink to prevent temp overshoots. It does not add moisture to the meat.
Yes, but that to add to what G. Wade said, the reality is that the added moisture helps things to cook more
evenly. And I don't just mean that the bark is slower to overcook compared to the inside of the meat. Wade's completely right. The difference can be obvious, depending at what cooking temp, but particularly with ribs at any and all temps, in my experience. However, I also mean that if you have several cuts on the cooker they tend to cook more at the same rate. In other words, let's say that you get a spike on the left side of the door where it might not seal too good. Well, water in the pan or not, anything is going to cook faster over that spot. Water in the pan is 212* from one side to the other though, and although that won't help much with things hanging out past the pan on a crowded grate, it definitely helps to some extent, and especially with what's over the pan where ideally, it
should be. But take this from a guy that is more prone to cook four or more butts than only two, or just as prone to cook six slabs of ribs as three. No, I'm
not the avg. backyard bbq guy, but the only thing that aggravates me more than when things finish at all hours of the afternoon is having end(s) of rib slabs way overcooked or a butt getting charred on one side. Yes, that happened on my last butt cook with a case of eight on and no water. Thankfully, it wasn't to the point of tasting burnt, but the point is that this has
never, ever, happened to me with water in the pan. But on the other hand, I've had great results without water in the pan. Personally, I don't care to go that route though, unless maybe I'm
foiling or cooking well over 250*.
The particular charcoal used matters
substantially in regard to this issue, though. I prefer lump, but Kingsford, particularly in the blue bag, is prone to ashing over and this serves to flatten out the bell curve of the temp changes over the course of a cook. Also, briquettes are easier to manage in terms of the evenness of the fire across the grate. There's no denying that, but I like my lump, and there's no comparison to Kingsford several hours into a cook. If I open the vent, the temp
is going to start to climb, no matter if it's several hours into the cook, or not, water in the pan or not. With Kingsford, if opening the vents doesn't help, I go and get my rubber mallet to tap on the legs and see if that helps. If it seems like I'm chasing rabbits, I'm really not. I'm just explaining why Kingsford works for a lot of folks that don't use water in the pan. Also, I'm sure that some folks have had the same experience as me. My 18.5", in particular, cooks so dang slow with water in the pan and Kingsford that I don't dare try that for butt or brisket cooks by day anymore. Like I said though, I like lump, and so unless you're using an ATC, I think there's no better heat sink than one that stays no hotter than 212*, particularly if cooking overnight on a long cook.
Regards,
Dave