keeps water cool instead of hot or frozen.
590026
I work outside.  I used to recycle/refill Gatorade bottles with water. It wasn't ideal but cheap.  I would leave my water in the car which doesn't have air conditioning.  The problem is the water would get hot in the summer and would freeze in the winter.  There's nothing like quenching your thurst with 115 degree water in the summer or have it freeze solid when it -20 degrees outside.  The Hydro Flask solved both problems.  It's also large enough to last all day.
1356150
Great way to keep beverages and food chilled on a hot day.  Worked perfectly and the drain on the bottom lets the water drain keeping the food free of water and easy for clean-up.
1816866
Keeps water cold for a very long time and pop off top is very convenient compared to the twist offs.  No spillage.
3338738
Looks awesome, and really keeps my water cold. I filled it on Monday morning and Wednesday it was still cold. I have not tried it with hot beverages yet, but I will be buying more for at home.
4546270
Seems to work fine.  I've used twice now and the water stays cool, not cold.  I'm not sure how long the cool will last though.  It's definitely better than a plain plastic bottle.
3398546
Keeps the water filtered in the frig.  Easy to install.
4695576
Works great in the winter months when the water would normally freeze.  The bowl is very large so it lasts 3-4 days without having to refill it.  We have two large bullogs who make a mess when they drink their water so I wanted a bowl I could leave outside of their doggy door on our patio.  The water doesn't overheat if you leave it plugged in on a warmer day either, which I was slightly worried about.  Just keeps it from freezing when it's cold out.  I've had it for a few months and it seems to be going strong.
1046303
Just got this to build a heated drip waterer for our chickens.  I sealed the heater in a water filled glass jar and dropped it in the water bucket. So far so good, it keeps the water nipples from freezing.  Coupled with the Thermo Cube it only remains on when needed.
2317907
I love this so much!  It keeps my water nice and icy cold for hours.
4681357
These make my life so much easier when trying to keep the water cool in my narrow necked water bottle. I was using a hammer and cracking up ice.. that made a mess and I wasted a lot of ice. These freeze quickly and pop out easily.. and they are BPA free.
3632948
Keeps water barely warm, just what we were looking for. I added a thermostatic unit to the outlet and that works very well with it.
1106406
Kept water from freezing in sub zero temps. Sides frost as the water level goes down but can't help that.
3837981
Love this for my tri bike. I can transport to our meet up location with the bottle in the locked position so it does not leak and then unlock for my ride. Water seems to stay cooler longer in this bottle. I typically put ice cubes in on hot days to ensure I have cold water for the majority of my ride. The 25 oz was a bit large for my medium tri bike frame so I had to order the 21 oz and they do the trick.
4036901
No condensation and keeps drinks colder longer than glass.
4104212
I bought this because I knew I was going on a long road
trip. I wanted it to store my water in, but also had to keep
my insulin cool. I haven't tried the heating part of it yet, but
the cooling worked perfectly. I read up on it a little, and did as
other people were saying. I plugged this into my home outlet the
day before leaving. Then I put already cold water in. This kept it
nice and cold. This holds plenty of bottles of waters, sandwiches etc.
I also purchased the adapter for home use. I love it.
1205701
Great to keep beer or water cool for a little longer than otherwise at room temperature or summer outside temps
4737527
I have used this about a month and really love it.  I switched to stainless because of reading it was better than plastic.  It doesnt sweat and keeps water cool.  Plus the design is neat and stands out so you know it is yours.