Here's why you really need to keep that water bottle on hand.

Water is super important for good health and, really, it helps with everything. Since about 60% of the human body is actually water, it needs to maintain hydration levels to fuel cells and keep the brain and body functioning.

You can stay hydrated by drinking water and certain foods can also help you stay hydrated, especially those with a high water content, such as cucumbers, watermelon, bell peppers and tomatoes. However, many of us aren't drinking nearly enough daily and are even drinking dehydrating sources, like sugar-sweetened beverages and booze, which can strip the body of hydration too.

So, what exactly happens to your body if you don't drink enough? Here are 10 not-so-pleasant side effects you might experience.

1. You Might Feel Low Energy

When dehydrated, you might notice your energy levels plummet, as water helps keep your mind alert and the body balanced. If you're not drinking enough during the day, that afternoon slump will hit even harder, and you might feel too tired to continue on with work or make it to your evening workout. Keep a water bottle on hand to remind you to consistently drink throughout the day.

2. You May Experience Mental Fog

Your brain needs water (our brain is about 80% water), and drinking enough keeps you mentally sharp, even long-term. A study in the journal Nutrients found that drinking water boosts brain health and prevents memory decline and mental drowsiness. If you're feeling foggy and are spacing out, chug some water and see if it helps.

3. It Might Increase Your Risk of Stroke

Water is good for your ticker, too. According to a study in BMC Cardiovascular Disorders, being dehydrated can raise risk of strokes and prolong recovery time, if you've had one. So, to keep your heart in tip-top-shape, pay attention to how much you're drinking. If your pee is dark yellow or you feel faint, drink some water pronto.

4. You May Be Moody

Dehydration can make you irritable and cranky, too. Two studies that took place at the University of Connecticut studied both men and women on a series of cognitive tests, and they saw that being dehydrated led them to a bad mood, drowsiness and even headaches. If you're feeling a bit irritable and aren't sure why, drink up and see if hydration helps!

5. It Might Lead to Overeating

Sometimes we confuse thirst with hunger, so drink up and see if that helps you distinguish what your body really needs. If you still feel hungry after that, then eat! It's important to listen to your body's cues and fuel it with what it needs.

6. It Could Slow Down Your Metabolism

Water is needed for every single function in the body, so when you're dehydrated, your metabolism naturally slows down—and with it, so do your energy levels. Staying properly hydrated can give you body what it needs to function so you can feel your best.

7. You May Experience Headaches

Since your brain needs water, when it's lacking it can lead to headaches and fatigue. So, before taking medication, have some water first and rest. That head pain might go away without you needing to take any other measures. Learn more about headache triggers and myths.

8. You May Damage Your Skin

Our skin needs water to stay healthy and look hydrated. Not drinking enough can increase the effects of aging. With insufficient water, collagen can crack, leading to fine lines and wrinkles. That's why people need moisturizing, hydrating products in a skin-care regimen to complement their water intake for that supple, soft look.

9. You May Have Weaker Workouts

When you're sweating, you're losing electrolytes and water, so it's important to drink before, during and after working out to replenish lost stores. As shown in a study in Physiological Reports, workouts might suffer from lack of water, and your body might not burn as much fat.

10. You May Gain Weight

A little weight gain is nothing to lose sleep over. That said, if it continues over time or is in the belly region in particular, it can put you at a greater risk for various chronic diseases, including diabetes, heart disease and more. Drinking water can even help you lose weight, especially if you're drinking it in place of sugary beverages or other higher-calorie drinks. Water is filling, so it can help you feel less hungry in between meals and snacks, although you shouldn't drink water as a meal replacement.