If there is a lot of empty space in the fridge, warm air can easily enter when the door is opened. Water-filled bottles help retain cold, which can play some role in keeping the internal temperature stable. However, the bottles must be placed in such a way that cold air circulation is not obstructed.

To reduce electricity consumption, it is important to avoid opening the fridge door unnecessarily, keeping it pressed right against the wall, and using damaged rubber seals on the door. It is also better not to put very hot food directly in the fridge; let it cool somewhat before storing it.

In addition, it is advised not to set a lower temperature than needed and not to let dust accumulate on the condenser coils of an old fridge. Keeping the fridge away from stoves, ovens, or places exposed to direct sunlight can also help reduce electricity consumption.

So, keeping water bottles can be a small trick. However, the fridge's age, model, size, temperature setting, and usage patterns have a greater impact on electricity consumption.