Water is the most important nutrient for every form of life on earth, and it makes up about 60% of your body weight. If your body is deficient in other nutrients, you might not have any symptoms for years, but without water, you will die in less than one week.

Your body is made up of trillions of cells. Inside and surrounding them are fluids made of chemicals suspended in water. Cells maintain a balance of fluids, depending on what they need, by water passing through the cell. Your body sends you signals to help maintain that balance, such as thirst or a dry mouth when you need more hydration. Bloating and frequent urination are signs that you might have too much water.

Water helps you regulate your body temperature. The middle layer of your skin, or dermis, stores most of your body’s water. When heat activates sweat glands, these glands bring that water to the surface of the skin as sweat. Once on the surface, the water evaporates, cooling your body and preventing overheating.

Water helps fight infection by flushing bacteria from your body via urine and by improving circulation of white blood cells and lymph in the body. It allows your cells to take in nutrients, and it also allows them to expel waste products. If you don’t drink enough water, toxins will build up, weakening your immune system. Water lubricates your joints, helping to prevent degeneration. It also lubricates your eyes and mouth, ensuring that they remain moist, and helping them to repel dirt, dust and parasites that might cause infection.

One of the most important functions of water is in the digestive system. Water helps form digestive enzymes and fluids, carries the enzymes that break down food, and dissolves minerals, vitamins, amino acids, glucose, and other nutrients. It helps carry these nutrients to the small intestine so that your body can use them. Water then helps to get rid of the waste. Your kidneys maintain your body’s chemical balance by filtering waste and excess fluid from the blood and excreting them through urine. Water is also the basis for blood, and helps carry oxygen to all the cells in the body, keeping the heart healthy by maintaining blood volume, concentration, and pressure. If your blood pressure or volume reaches too low of a level, or if your bodily fluids start to get too concentrated, your kidneys begin to slow down to retain water when the body needs it.

You can calculate your personalized water needs with this hydration calculator. My results indicated that I need to drink 74 ounces (9 1/4 cups) or 2.2 liters, but if I eat a healthy diet (and I do), about 20 percent of my water may come from the foods I eat, so I can drink 59.2 ounces (7.4 cups) of water today, or 1.8 liters. When you’re ill, during hot weather, and during strenuous exercise, you should drink even more water.  Physical activity can actually make you less sensitive to thirst, even though your body needs more water.

Plain water is the best way to hydrate your body, but there is water in every liquid that you drink as well as in many foods. Crunchy vegetables such as celery, cucumbers, lettuce, and carrots are made of 75 to 90% water. Watermelons, grapes, and oranges are full of water. Coffee and many sodas contain water, but they also contain caffeine, which may stimulate your kidneys to excrete extra liquid, as well as increase blood pressure and heart rate. Coffee also creates some acid in the digestive system, which can aggravate ulcers and acid reflux disease. Avoid sugary drinks, which contain more calories than nutritional value. All these beverages can contribute to your daily water needs, but they have other effects on your body to consider before making them your main source of hydration.

Industrialized countries treat their water, but some people do their own filtering at home. Home filtration systems can come in many forms. They can be attached to your faucet or water pipes or as a handheld pitcher with a filter inside. There are also different kinds of filtering systems, including carbon, reverse osmosis, and distillation. These systems can remove unwanted additives such as bacteria and other contaminants such as arsenic and heavy metals. The U.S. Environmental Protection Agency’s website is a good place to find local drinking water information.

The Food and Drug Administration sets standards for bottled water, which are the same for public water systems. Some bottled water comes from groundwater sources like springs or wells. It is most often purified with a gas called ozone, which in some instances is considered a pollutant, but is also an effective treatment for some contaminants. Twenty-five percent of bottled water is estimated to come from municipal sources (city water).  Companies are required by law to state the source of the water they bottle, and despite being regulated by the FDA, contaminants like arsenic have been found in many brands of bottled water.

So drink up, and stay healthy!