Keeping track of water volume?

Hello!

I am thinking up an idea for a project and I need to keep track of changes in volume of water. The water would be in a water bottle and the sensor could not be inside the actual water bottle. So right now I am thinking of something that would maybe weigh the water bottle? Does anyone have any ideas of how to keep track to changes in volume of water?

I am very new to this all, so things that might seem very basic would probably still be very helpful to me.

Thanks!

a pressure sensor.

For level switches you can also use capacitive sensors on the outside - simple but providing only a few levels of course. Weighing the bottle is another good option.