We probably don't give it much thought because it is so widely available. However, inadequate supply of water is critical to our health. If we were deprived of many vitamins or minerals we might survive for months or even years. But without water we would last only a few days. Water may be particularly important for individuals who sweat a great deal.
Examples are farmers, construction workers, and others who work under hot conditions.
The body needs water so that it can cool off during the sweating process. If sweat losses are high, heat exhaustion may result. Furthermore, performance may be compromised by losses as little as 3 percent of the body weight. For a 165 pound person that is a 5 pound loss. Unfortunately, thirst is not always a reliable indicator of how much water you should drink.