With the holidays behind us but the coldest part of winter setting in, now is the time of year many begin fantasizing about days warm enough to slide into a swimming pool to cool off…snorkeling in crystal blue waves…dashing through a sprinkler with the kids in the back yard…filling water balloons for the annual end of school extravaganza…

Water covers about two-thirds of our planet and also makes up about two-thirds of our bodies. That makes it an important part of our lives beyond all the fun we have playing in it. Most people are aware of the recommendation to drink at least eight glasses of water a day, though many Americans would probably admit they don’t achieve that on a regular basis.

Though we know we need it, what does water do in our bodies? Let’s take a look.

We ingest all the water our bodies need through our digestive tract, along with food and other nutrients. Water passes through the mouth down the esophagus and through the stomach into the small intestine. The small intestine absorbs all the water we ingest daily (about 1-2 liters), along with 6-7 liters of fluids from secretions from the stomach, salivary glands, pancreas, liver, and small intestine itself. That’s a lot of fluid!

The small intestine is responsible for absorbing nutrients from the food you eat. Water follows the nutrients into the cells of the small intestinal lining. The nutrients, with the water still following, then pass into the small blood vessels lining the gastrointestinal tract, which then connects to the vasculature of the entire body. The small intestine reabsorbs and recycles most of the water secreted so as to not cause dehydration.

By the time food and water reach the colon, about 80% of the water has been absorbed by the small intestine. The colon’s job is to keep just the right amount of water to allow for healthy stool to pass easily from the body and reabsorb that last little bit into the body. Ingenious, right?

So, what happens if you get a little too much water in your body, provided you’re otherwise healthy?

Your body is very good at keeping conditions inside it just right for optimal functioning. Thus, the small intestine absorbs the extra water into the blood stream and the kidneys excrete any that is not needed in urine. Your stool should be just right, not runny and not hard.

What happens if you get too little water in your body?

Your body then tries to hang onto every last drop to maintain that healthy balance. That’s when you may notice more concentrated urine that’s dark yellow. It can also lead to dry, difficult to pass stools.

What about extreme cases of water loss, like when you get food poisoning?

In a disease state such as this, your body attempts to flush the offending organism out using vomiting and diarrhea. While this is a very unpleasant experience for you, it’s your body doing its job to keep you safe and healthy in the long term.

But in persistent disease states (either longstanding food poisoning or chronic disease), the body can use too much of your body fluid trying to flush out the offending organism and you can become dehydrated. When you’re dehydrated, the water, nutrients, and electrolytes in your body become unbalanced, leading to more severe disease. This is why your doctor often tells you to keep drinking fluids when you’re sick, though small sips are more likely to stay down. If you cannot keep anything down, your doctor may recommend that you go to the hospital for fluids via intravenous line, or IV. Medications to calm vomiting and diarrhea can also allow your body a reprieve to absorb water it has lost back in.

Bottom line: water is important. Drink up!