One very good way to know if you are properly hydrated to to look at the color of your urine. If it is a bright or dark yellow you are most likely dehydrated. When your body is properly hydrated the color of your urine is a very pale light yellow.
my pee is almost always a light/pale yellow. love me some water!
im going to print this out shove it in my pocket and when i pee whip it out and compare the colors