There are a few ways to determine if water has frozen in a freezer overnight:
Visual inspection: Check for visible signs of ice formation. Open the freezer door and look for ice crystals or frost on the walls, shelves, or around the water container.
Texture and consistency: If you suspect that water has frozen, touch the container or surface where the water was placed. If it feels solid, hard, or icy, it is likely frozen.
Movement or lack thereof: Gently agitate the container or try to move the water. If it appears rigid or does not move freely, it has likely frozen.
Thermometer reading: Use a freezer thermometer to measure the temperature inside the freezer. If the temperature is below the freezing point of water (0°C or 32°F), it indicates that water would freeze under those conditions.
Ice formation in other items: Check for ice formation in other items stored in the freezer, such as ice cream or liquids. If these items show signs of freezing or have become solid, it suggests that water has also frozen.
Remember that freezing times can vary depending on the volume and container material, so it's possible that water may not freeze completely overnight if the conditions are borderline freezing.