I might not have mentioned this before, but like you mentioned, water hydrates your body and makes your body cells turgid. This makes you strong during meditation. Also you can try the following.
1. Do some yoga of me or stretching before meditation.
2. Take a rest maybe a nap so you can be more awake as you meditate
3. During the day, try to keep your mind at the center in your activities. This will help you cultivate mindfulness.
Wish you all the best in your other session.
You will with consistent meditation improve your experience.
:)
Cheers.