This one's a no-brainer, and yet many of us tend to underestimate how much water we need. In fact, researched shared by CBS Miami says as much as 75 percent of Americans are walking around chronically dehydrated. Because our bodies are so overwhelmingly composed of water, when we deprive ourselves of H20, Prevention says we can stop sweating, lose salts, lose energy... and get really, really thirsty. If you're feeling thirsty, perhaps the likeliest explanation is dehydration. So, drink up!

Ah, yes. Along with debilitating cramps, mood swings, and wild cravings, you might also experience excessive thirst during that time of the month. According to the Center for Young Women's Health, this is actually a pretty common symptom of PMS and menstruation. Dr. Orli Etingin of Everyday Health explains that it's likely due to the loss of fluids and blood. Even though your period might have you feeling stupid bloated, try to get more water into your system. It'll help fend off that feeling of weakness you get during your period, too.

The food you're eating could be to blame for your constant thirst. If you're eating a lot of food high in sodium, for example, it could be interrupting the balance of fluids in your body, says Livestrong. When your sodium gets too high, your body tells your kidneys to get rid of some of it by peeing it out. Your body will ultimately nudge you with feelings of thirst to help balance things out again.

Harvard Health Publishing says dryness in the mouth can be caused by nervousness, anxiety, and breathing with your mouth open — something many of us do when we're sleeping. Colgate adds your medication could be the cause. Ultimately, it all means the glands in your mouth that produce saliva can't function properly. You might have to make some changes in your life to stop encouraging your dry mouth, but it certainly beats the alternative.

The Mayo Clinic explains anemia as a condition in which you're lacking healthy red blood cells and can't get enough oxygen to all of your body's tissues. More severe anemia might be accompanied by excessive thirst and, perhaps unsurprisingly, increased sweating, says the U.S. Department of Health and Human Services. This happens because your body is losing too much fluid, since you're losing red blood cells faster than you can create them.

Feeling thirsty and peeing a lot are common symptoms of diabetes, according to the Mayo Clinic. This happens because your kidneys have to work harder to manage all the extra sugar in your blood. Once they've hit their limit, you pee out the remaining sugar, plus other fluids from your tissues that are excreted along with it. This will make you pee even more. In the end, you're dehydrated and craving water... and then you'll pee more.

If you were recently fighting a cold or the flu, you were probably a snotty mess. Add in diarrhea, vomiting, and sweating, and you probably lost a lot more fluids than you typically do. The result? You're all dried out. Make sure that when you're replacing fluids, you're making smart choices; according to a recent study, sports drinks may not be your best option when it comes to rehydrating.

Having an overactive thyroid could be the reason you're always thirsty, says Harvard Health Publishing. Hyperthyroidism causes your body to produce too much thyroxine, according to Patient.info, and as a result, a lot of your body's function kick into overdrive. You might feel nervous, restless, have tremors, be out of breath, lose weight, and always feel hungry or thirsty.