A good rule of thumb is to drink 1mL of water per calorie burned minimum. Since the average person burns between 1200 calories and 2200 calories per day without including exercise. Assume the minimum you should drink per day is about 2 liters or 64 oz or 8 glasses of water. If you are exercising, you should add 1mL per calorie burned so 0.5 or 1 liter for a typical workout and more if you are completing higher intensity workouts.
One way to know you are hydrated, other than tracking your water intake, is to be sure of how often you are urinating. You should urinate 3-5 times per day and the urine should be pale yellow or clear if you are hydrated. Caffeine and soda can skew these urination readings since they are both diuretics and will make you urinate more often while also dehydrating you. Be sure to increase your water intake if you are drinking caffeines or sodas. Adding flavor additives to your water only increase the chemicals in your water, acting as a soda. Water with additives and sodas and juices do not count as you water intake for the day. If you must add anything to your water to flavor it, try cucumber, lemon, lime, grapefruit, or mint. Natural additives are better than chemicals if you MUST add anything.
Some of the signs of acute dehydration include fatigue, hunger, joint aches, dry skin, wrinkles, dark urine, and constipation. Signs of chronic dehydration include digestion problems, confusion, anxiety, urinary tract infections, premature aging, and increase in cholesterol.
My suggestion is to get a great spill-proof water bottle to stick in your bag and take it everywhere you go. Make sure to have finished at least one full liter in the morning and at least one in the afternoon.
Hope this helps you all understand how to better keep yourself hydrated! Enjoy the warmer weather :)