Water is "the most indispensable nutrient," according to the book "Nutrition: Concepts and Controversies," by Frances Sienkiewicz Sizer and other authors. Water carries nutrients throughout the body and helps regulate chemical reactions. Because water is lost in a variety of bodily processes, like sweating and urinating, you need to replenish your water supply regularly to avoid dehydration.

Although individual needs vary based on climate, activity level, altitude and diet, the National Institutes of Health have established general guidelines for healthy adults. Adult men who live in temperate climates should consume about 13 cups of water from all beverages, and adult women need about 9 cups. These recommendations include water from all beverages, and account for about 80 percent of total water needs. The other 20 percent is obtained from food sources. Many food sources like tomatoes, melons, celery and oranges are actually 85 to 95 percent water.

Although some of your daily total water intake comes from foods and other beverages, the majority of your intake comes from drinking water. For this reason, as noted by the Mayo Clinic, most doctors recommend that adults drink eight to nine cups of water each day. One easy way to remember this recommendation is to keep in mind the "8-by-8" rule: eight 8-oz servings of water each day. If you live in a hot climate or exercise regularly, you might need to drink even more.

If you find it difficult to meet these recommendations, a few simple strategies might help. Always carry a bottle of water with you when you leave the house for a long period of time. This will help you stay hydrated and may also decrease the temptation to buy high-calorie, high-sugar beverages while you are out. If the taste of water doesn't appeal to you, add a bit of lime or lemon for added flavor. Finally, opt for water instead of soda or sweetened drinks when you eat out at restaurants, both to ensure adequate hydration and avoid high calorie intake.

Dehydration can be life-threatening in serious cases. When the body loses too much water, through excessive urination, vomiting, diarrhea, fever or sweating, you might experience symptoms like dry mouth, decreased urination, lack of tears when crying, sunken eyes and lethargy. Mild dehydration can usually be treated by increased fluid intake. Prevent dehydration by always drinking when you are thirsty and by increasing your fluid intake during sickness, exercise, pregnancy, lactation and in high temperatures and altitudes.