When you buy Amazon Fresh, if it contains anything cold, Amazon will include many packs to keep it cold. Our first time was a decently large order and it contained 8 (!) of such packs. They don't have a program to return these things. It's not just water inside but some other substance that shouldn't be casually thrown out. Suffice to say it was also our last order. I wouldn't say we're particularly more garbage-conscious than most but that was just absurd.
To me, that should be illegal without some kind of reuse program.
Most of the cold gel-packs actually are just water inside. We had one of the packs (with the little green gel beads) split open and our infant ate some of the beads, but when we called poison control they were like "Yeah, the beads are just tap water wrapped in plastic. The water's harmless, and the plastic will just pass through his digestive system. In rare cases the water can have bacteria in it, so watch out for signs of mild food poisoning, but otherwise he should be fine." I guess they individually wrap the water so that it can continue to conform to the shape of whatever you wrap it around, plus it melts more slowly and the temperature release is more controlled. Probably also helps them charge more if the customer believes it's some fancy chemical rather than just water - no manufacturer ever says exactly what's in their cold packs.
Not exactly great for the environment (how does an ice pack manage to have more plastic inside than the entire rest of the packaging?), but yes, you can casually throw them out. Also a brilliant example of marketing and customer deception.
This may not have always been the case, per the other reply to this comment. In my experience that is correct, because we cut them open and there was no such beads, just an opaque gel that, while could've been simply water, didn't seem like it (I've never seen "pure" water in a gelatinous form). I only recall reading that it was drain-safe, so maybe that supports the water theory (though we put much more than water down drains), or at least some mostly-safe substance.
That scheme didn't last very long, and they've changed a couple times since then. For a while it was similar packs, but filled with water, and the pack said to just pour it down the drain. And now they send packs of dry ice along with frozen food, and frozen bottles of water along with refrigerated food. The dry ice just sublimates away (and the cardboard it's in is recyclable), and the bottled water is at least slightly valuable as a product.
Found this use of it interesting (from the Wikipedia article about dry ice):
>Plumbers use equipment that forces pressurised liquid CO2 into a jacket around a pipe. The dry ice formed causes the water to freeze, forming an ice plug, allowing them to perform repairs without turning off the water mains. This technique can be used on pipes up to 4 inches (100 mm) in diameter.[23]
The main point is that nobody produces (at industrial scale) CO2 just to make dry ice. It's a byproduct of other process that is normally released to the atmosphere, but in this case the release is delayed for a few days.
To me, that should be illegal without some kind of reuse program.