You know it’s important to make sure your child eats well. But is she drinking enough, too?

A new study from Harvard’s T.H. Chan School of Public Health has found that more than half of American children and teens aren’t sufficiently hydrated — most likely because they’re not drinking enough water.

Getting too little fluid won’t just cause a kid to have a dry mouth. “Dehydration affects the whole body, particularly the heart and brain,” says Ashanti Woods, MD, an attending physician at Mercy Medical Center, Family Health Centers of Baltimore, in Maryland. As blood volume drops, the heart must work harder to pump, he explains, and brain neurons may grow sluggish.

Dehydration also can interfere with metabolism, circulation, elimination of waste and temperature regulation. Being even slightly dehydrated can make kids (and adults) cranky and headachy and less able to perform physical tasks efficiently or think clearly.

Related: 7 Signs You Need a Drink (of Water!)

Why aren’t kids getting their fill of fluids? “I partly blame tight schedules and limited breaks,” says Woods. During the school year — and even during summer for children who go to camp or are out with friends all day — kids often skip breakfast, spend mornings in class or doing some other activity and so lunchtime is their first opportunity to drink anything. The next chance they have to get a good dose of fluids may be hours later, once they’re home.

Fill ‘er up: 5 ways to keep a child hydrated

Woods believes another reason kids become dehydrated is because parents and other adults (teachers, camp counselors) aren’t always around or don’t always think to remind them to drink throughout the day. Here are five ways to help a child get enough fluid each day.

1.  Learn the signs of dehydration. “They can be tough to spot — even doctors have trouble sometimes,” says Woods. “If your child is irritable, assume she isn’t drinking enough. Dry, cracked lips are another sign.” So is lack of perspiration: “When you pick up your child after an active day at camp, she should be a sweaty mess,” he says.

2.  Teach your kid to monitor her pee. Teenagers and even tweens can get into the habit of checking the color of their urine to make sure they’re drinking enough. “It should be clear to light yellow,” says Woods. “If urine is dark yellow, it means a child isn’t getting enough water.

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3. Make it easy to get enough H20, even on the go. Hand your kid a fresh bottle of cold water before she walks out the door each day. If disposable plastic bottles are against your environment-saving instincts, let your child pick out a reusable bottle with a wide, screw-on lid (for easy cleaning and to reduce the risk of bacteria growth that’s higher in plastic pop-up tops).

4.  Defend her from distractions. A kid doesn’t have to constantly sip water to stay hydrated; a few generous gulps every hour or hour and a half will do the trick. But it can be tough for an active child to keep track of when she should take a swig. If yours has a phone, this is one time technology can save the day, says Woods: “Have your kid set reminders to go off every sixty to ninety minutes to nudge her to drink.”

5.  Supplement plain water with tasty alternatives. Many fruits and vegetables are made up largely of fluid. Grapes, melons and tomatoes are 90 to 95 percent water, for example. Make them part of your child’s daily diet. Pack them in her lunch and keep them handy for snacks.

Steer your child away from juice and soda (except as once-in-awhile-treats). “The sugars in these beverages can lead to tooth decay,” says Woods. And of course the added calories can cause unwanted weight gain.

There’s no need to pump a kid full of energy drinks either. While they can replace electrolytes lost after a period of intense activity — a long, hot baseball game, for example — a big glass of ice-cold milk is just as good.

Related: Water Intoxication: The Surprising Dangers of Overhydration