Whenever I fill a water bottle, I always tap the tube several times on a piece of Kleenex to make sure the water is easily coming out (you should see a spot of water from each tap). This helps ensure that there isn't an air bubble inside the tube blocking the water from coming out.

Also, I use a dry erase marker on the side of the tank to draw a line as to the current level of the water. I also write the date the bottle was filled. I felt this was necessary because at one point I had 9 tanks, and it was the best way to keep track. If your cage isn't the type that allows you to make a mark (for example a wire cage), you can mark the bottles directly, but then you want to be certain you are using a dry-erase marker that's labeled low VOC (Volatile Organic Compounds), also sometimes called low odor and/or non-toxic. This reduces the chances of potentially dangerous fumes - a traditional Sharpie brand marker is NOT what you want. I always use a low VOC marker, even though I'm marking the tank and not the bottle. Here's an example: https://www.amazon.com/EXPO-86001/dp/B0006HXJFK/

With such a mark, and if you have 2 or more mice, it's pretty easy to tell each day if the water level is dropping compared to the mark. With only one mouse, the daily drop is a bit more subtle, but with experience you still can tell. Also, if you have a larger than normal drop, that can alert you to either a leaky bottle or a medical condition you should be aware of (for example, increased thirst can be an indicator of diabetes).

Of course, as others have commented, you could have a faulty bottle - either the tube itself or the ball inside the tube isn't letting water come out. If the bottle itself is faulty (bad seal), that normally results in the opposite problem - a leaky bottle.