The energetic benefits of water are a big reason for why athletes drink so much of it. With more energy, you’re able to exercise more. As a consequence, more of the “feel good” hormones (that come from exercise) are able to fire through your brain to improve your overall mood.
Keep in mind that your mood also has a direct impact on how productive you can be throughout the day. People with elevated moods often experience higher levels of productivity in contrast to those with lower moods. It sort of ties into how people suffering from major depression often experience a lack of motivation to do anything commonly seen as enjoyable. The sad affect takes over and the mind loses the willingness to fight back. It’s awful but it happens.