Drinking of water is a variable factor which  depend upon various factors such as, climate, age, Health and fitness, physical labours and many more. Any thing when used excessive, may caused for health hazards.

Based on the literature on and experience with the San/Bushmen in the Kalahari my broad hypothesis would be that even at high physical activity like chasing prey on foot for hours or days in a low atmospheric humidity environment, Homo sapiens can do with far less than a liter of (drinking) water per day over long periods without health hazards. 

In more detail, habituation/training and behavioral adaptation (e.g. not drinking during the heat of the day; walking and working at night; resting in the shade during the day) needs to be included in testing such hypothesis. Other variables are the water uptake through fluids from prey (e.g. blood), fruits and roots. A further element to consider on the potential health effect is the mineral content of the drinking water. Possibly, high calcium content maybe a factor in developing kidney stones.  Finally, the role of water in the excretion of potentially poisonous substances (e.g. urea) deserve attention as well. After pure protein meals following a successful hunt, more fluids  may be needed to wash out the urea than on an average day. Similarly, drinking several liters of pure spring or rain water may deplete sapiens from salts and other minerals. Salt is so essential that it used to be the first request upon arrival by car in a San settlement.

To take another extreme, competitive cycling at midday in May, like in the Giro d'Italia, will certainly require more than a liter of (isotonic) drinks a day. 

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