To increase body water percentage:
Drink a decent amount of water throughout the day.
Drink fluids before you're thirsty.
Eat plenty of fresh fruits and vegetables.
More muscular people tend to have a higher water content percentage, as muscles contain more (~70%) water than fat tissue (~10%). Getting more muscular might be a way.
Get a mobile app that would remind you to drink water.
Add flavor to your water to make it taste better (citrus juice, artificial flavors).
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