My take on the water bottles is that they discard and buy new ones at each town or village they come to. There is no lack of potable or treatable water on their route. Most of it is thru or near rain forest. It's pretty darn wet along the SE coast of Alaska. I'll have the kid ask them that question.

The weather along the coast that they are traveling isn't much worse than mine in SE PA. The killer is the reduced sunlight. Cordova is down to just 6 hours a day now and only a couple of hours of strong light, plus it's mostly overcast all the time.

It probably rains 300 days a year there. That and the dark winters drive a lot of residents south for the winter.

PS. Summers there aren't a lot warmer. Average daytime high in July was in the 50's, occasional foray's into the 60's. Lots of sun however...