8 Signs of Dehydration You Shouldn't Ignore

1. Thirst

If you feel thirsty, you're probably already a bit dehydrated, especially if you are age 65 or older. “The amount of dehydration required for that sense of thirst to kick in is going to happen a lot later than when you were younger,” Hashmi explains.

Even if you don't feel thirsty, older adults should drink throughout the day, he advises. Aim for at least 48 ounces of fluid (six 8-ounce glasses) a day – and more if you're physically active. Juices, sports drinks, noncaffeinated sodas and flavored waters or seltzers all count toward your fluid intake, Hashmi says. You can also boost your intake with foods containing a lot of water such as soups, watermelon and cucumber.

2. Dark urine

The more fluid in your body, the clearer your urine will be. Your urine should be “almost the same color as tap water if you're well hydrated,” Hashmi says.

If your urine turns a dark yellow or brownish color, or if it has a stronger odor than normal, that's likely an early sign of dehydration, and you need to drink more water.

3. Dizziness or fainting

Although dizziness can be a symptom of many different conditions, it is a classic sign of dehydration, Atkinson says. When you're dehydrated, you don't have enough fluid in your blood vessels. You feel dizzy because “you're not getting as much blood flow to the brain,” he explains.

You're most likely to feel dizzy when you sit up after lying down, or stand up from sitting. If the blood flow to your brain drops significantly, you may notice a darkness in front of your eyes, Hashmi says. That may be a sign you're about to pass out from dehydration.

4. Muscle cramps or weakness

Another sign of dehydration is a feeling of weakness in certain muscles or severe muscle cramps. The cramps can be caused by electrolyte imbalances and reduced blood flow to those muscles.

Cramps can happen while you're exercising, or you may wake up in the middle of the night with cramping in your calf muscles. “It can be severe enough that it won't let you sleep,” Hashmi says.

5. Constipation or less frequent urination

Water helps flush toxins out of your body and keeps your digestive system running smoothly. If you're adequately hydrating, you should be urinating every two or three hours and having regular bowel movements, Hashmi says. “If you're not going to the bathroom the usual number of times, that can indicate a problem,” he says.

6. Dry skin or lack of skin elasticity

Dehydration causes skin to be dry and look sunken in some areas, such as under your eyes. Your skin will also have less elasticity than normal. If you are caring for someone who is frail, one way to tell if they are getting dehydrated is to gently pinch or press the skin on their arm. “When you touch their skin, it may not spring back as easily as before,” Atkinson says. “It can be very pronounced.”

7. Dry mouth

Dehydration also reduces saliva production. If you suspect someone is dehydrated, pay attention to the inside of their mouth, Atkinson says. “Their tongue should have a glisten to it,” he says. “In extreme (dehydration) cases, you may notice sores in their mouth that go along with not having enough fluid.”

8. Fatigue, headache or confusion

Low blood flow due to dehydration can cause a headache, tiredness and weakness. Or you may just feel a little less sharp than usual. If you're a caregiver for someone who seems confused, don't rule out dehydration as a cause, Hashmi says: “A lot of things can cause confusion; maybe mom or dad has an infection. But it could also be that they're getting dehydrated, and their blood pressure has dropped. Sometimes when we give them fluid, it's amazing what happens.”

Michelle Crouch is a contributing writer who has covered health and personal finance for some of the nation's top consumer publications. Her work has appeared in Reader's Digest, Real Simple, Prevention, The Washington Post and The New York Times.