Drinking sufficient water is one of the best habits to form to lose weight. The calorie free elixir keeps several illnesses at bay.
Not getting enough hydration can cause fatigue, constipation, headaches, impose extra work on kidneys for excreting toxic by-products, cause heartburn, stomach pain, depression etc.
There is no recommendation for drinking water for a healthy human being, but for the smooth functioning of the bodily functions, the rule of the thumb is 8 x 8. That is, 8 cups of fluids (water based) with each cup being of 8 ounce measure.
Athletes, people at altitudes higher than 2500 metres or in humid hot environment including heated indoors, pregnant and lactating women need higher intake of fluids. Also, anyone exercising or spending time out under the sun will need to drink more fluids.