You say you've read my posts - so you've read that the last two times I've done day hikes at GC was with a 1 gallon hydration pack. You also read that I am by no means dismissing the heat and dryness of GC and I know there is a big difference in climate between the humidity of south Florida and the dryness of Arizona deserts. If you like I can go into chapter and verse with full details on what I know and what to worry about with regards to that - but that would make the post extremely long.

I also mentioned in my OP that I WAS and AM concerned about how much water to worry about carrying. I'm planning on 1 gallon (9lbs) depending on the availability of water. I have spent alot of time researching and find those posting about their trips, on average, carry 1.5 to 2 liters and that is enough to get them from one water source to the next in an effort to keep their weight down in the packs. Some say there is plenty of water on North Kiabob while the Nat Parks say no. I know there is water at cottonwood and at Supia tunnel, and presumably at Rainbow falls (bringing filter to filter it there if necessary).

Likewise - considering Bright Angel - mostly shaded. Starting at 4 or 5am we should be to BA Camp well before noon where we can shed the pack and relax by the river and enjoy dinner (and quite possibly lunch) at PR. Thus before the heat of the day. And same with going from BAC to COT will be done before noon, getting us out of the depths of the canyon before the heat of the day sets in. Cot to North Rim is at high enough altitiudes that you really start getting the cooler weather from the north rim.

As I said originally - I am NOT trying to dismiss the heat and conditions of GC. I am well aware of them and we are planning for them. You all say that planning on a 40 to 50 lb pack is possibly too heavy for this trip. Considering 10lbs of it is going towards hydration, thats bring the pack down to 30lbs or so for food, gear and supplies.

IF - and only IF there is guarenteed ample water supplies (equal or greater than that on Bright Angel) then I might consider cutting back to 1.5 to 2 liters. But at that, I'd only do it if we are guarenteed water at least every 2 miles.

I certainly would plan to err on the side of caution with this trip and in regards to hydration. That is my BIGGEST health concern of this while trip. Hence my reasoning for wanting to train the entire party to carry heavy packs over long distances.

By the by - based on historic records - June is not the hottest month in Arizona, or under the rim. July/Aug are. Just to clarify. But I certainly know that a heat wave can hit ANY TIME causing temps to soar beyond 110.