The whole taking a dslr and additional lens thing to me isn't worth it. It's significant weight, you have to worry about water and shaking the crap out of good equipment, and from my personal experience, it's just not worth it.
I'm biased as I've never carried good photo equipment on bike trips over 30 years. To me it's a bike trip, not a photo trip, and point and shoots have always been the correct compromise for me.

as mentioned, I'd put more of an emphasis on water, but as I'm not familiar with the area and temps, I can't really comment on how much you need.
all I know is that as you said, not enough water is a real, real drag and not fun at all.