A few weeks ago I picked up a couple of pint-sized Nalgene water bottles. Possibly I'm following a trend: the younger people at my Naval Reserve unit have been bringing these bottles in during their training.
One of them liked the firefly yellow color, which I thought bizarre because it reminds my of a specimen bottle for urine testing. The first one I bought was violet, because in certain kinds of light it turns into a vivid blue (a more appropriate color for water). The second one was the more stable slate blue. (I take the blue bottle to Reserve training because as far as I can tell no one else is using that color.)
Actually I find them quite useful. Certainly the water doesn't taste like it just came out of an Army canteen. And they're a convenient size to tuck into a shoulder bag; if you fill it at home with filtered tap water, you won't need to buy bottled water during the day. It may be a fashion trend, but it's one of those trends with practical value.
There've been some concerns expressed over the product safety of these bottles, but I'm inclined to dismiss them. Animal research is a useful indicator, but the applicability to humans is minimal at best.
Anyway, if you haven't done so already, you may want to think about Nalgenes for carrying water if you're working out or need water refreshment during the day.