Got a portable charger, a good insulation material, maybe some salt or sugar, you can keep that water from freezing. Wrap the container in the insulation, place it inside a reflective cooler or even a small battery pack set to a low heat mode if you have one. Adding a bit of salt lowers the freezing point, so a pinch of it in the water before you close it can keep it liquid a bit longer. If you have a solar panel, keep the charger running and use a small resistor or a low‑power LED to generate a little heat. Keep the whole thing out of direct frost and you’ll be fine.