I'm debating getting one of those day packs that has a water system built in. We were walking around the lake yesterday afternoon, and it was really hot. I hadn't brought my backpack with me (even though I should) because I didn't feel like packing things in it. I never bring a water bottle on my walks because I don't want to carry it and bother with it.
If I had my pack with a water bottle in it, I'd have to stop and get it out to take a drink. Which means I just wouldn't.
So I'm wondering if I would actually drink out of one of these packs. I don't know if I'd go for it with an actual long term or overnight pack, but for a day pack it seems highly useful.