There are many excuses but no genuine reasons. Water is fat- free and contains no calories. Almost every bodily process needs water to function. Your body needs water in greater supply than any other nutrient. Water regulates your body temperature, it transports oxygen and other nutrients and it provides a cushion for joints and helps to protect organs.
Water is the basis for blood, saliva, digestive juices and urine.
By the time we feel thirsty, we are already slightly dehydrated. It's like adding oil to the crank case in your car, by the time the light comes on, you are already at risk of burning up the engine, which is very low. The amount needed by each person varies. Because your body does not store water, a fresh supply is needed daily. The average adult loses about 80 ounces of water per day.