I did 15 miles (my longest distance ever) with my 18-20lb terrier mix a couple weekends ago in nice weather. Towards the end he showed signs of tiring, I wouldn't push it much further. How did I know he was tiring? #1 was I keep him on a retractable leash and normally he is at the end of the leash looking back at me like I am holding him back, he will get all ancy if he hears a lizard or squirrel off the side of the trail. Towards the end of the 15 miles he was lagging behind and ignoring lizards.
In my opinion it is irresponsible for a TON of reasons to hike with a dog off leash. Your dog could go after dangerous wildlife (bears, skunks, porcupine, poisonous snake, etc), your dog could harass wildlife, harass other hikers, harass other hikers dogs. Most dogs will tire out running up ahead then back to you, effectively doubling or more the distance they hike so if you are going 15 they are going 30-45 miles. Also puddles, most dogs will drink out of nasty, stale, mosquito infested puddles which I have read there are several fatal diseases they can get from those. I could probably go on but suffice it to say I believe in leashing my dog. I like the retractable leashes because it manages the slack so I don't have to. If I see other hikers coming I call him back in and lock him in by my side. Also I like him up ahead of me a good bit so I am not tripping over him if he stops to smell something. When I get to camp I can put the handle on a stick, stake it to the ground, whatever and the leash manages the slack and he can still move around.
As far as water, I let him drink straight from clean looking streams and moving water sources, I use the leash to not allow him to drink from puddles and stagnant water (which he will try to do).
As far as a water bowl, I carry either a small disposable Tupperware container (the thin kind) in my pocket so I can easily get to it, give him some water.
With my dog he won't eat his dry food when out hiking, he gets excited when traveling, hiking, hunting, whatever and just will go days without eating so I bring him those small packets of soft food to put on his dry food, mix it up then he eats it.
Sleeping he sleeps on my backpack with my driducks rain jacket, fleece, shirt or whatever under him so he has something to sink into. If it is cold I might bring him a little piece of a blanket I cut up for him.
Final advice is pay attention to the subtle differences in how your dog is acting. Dogs usually love their humans and will do anything for them include dying for them. I have grown up around hunting and hunting dogs and I have seen retrievers sitting in freezing water all day with ice forming on their private parts, ears and face but if you tried to get them to stop hunting they will pull away and fight you to stay doing what they are doing. I have heard stories of hog hunting dogs, pit bulls and terriers that will get slashes and have their guts hanging out and want to keep going, keep hunting. Dogs don't always know what the deal is they just love doing outdoor stuff, love being with their human, love pleasing their human so just because your dog is up for doing something, don't take that as a sure sign that they are fine doing it.