Definitely. I’ve never used it for anything, but water. But I don’t see that it would be a problem with milk. I usually put ice in my water and the ice stays solid for a good 10 hrs. I’ve also filled it with cold water without ice and it has kept the water cold over night.

I would say, “yes!” I have only used water with ice, but when I put only water in it, as long as it was cold water put in my water stayed cold for at least 8 hours without ice added!