You can live without water three to four days on average.

Living without Water for Two Weeks 

In the spring of 2010, an 83-year-old Indian holy man, Prahlad Jani, confounded experts seeking a definitive answer to this question by living without water or food for a supervised period of two weeks. The experiment, conducted at a hospital in Ahmedabad, India under the auspices of the country's Defense Research and Development Organization (DRDO), showed that over the course of 15 days, Jani did not once consume food, water, or go to the bathroom. A neurologist overseeing the experiment has stated that neither he nor his fellow scientists can explain Jani's superhuman feat.

The Average Joe 

For the great majority of humans who do not have the luxury of relying on science-confounding yogic powers, the amount of time a person can live without water before dying is generally accepted to be three to four days. While reserves of fat and protein in the muscles of a human body can be tapped to varying degrees by different-sized people over the course of many weeks in place of food, water is an essential and irreplaceable component that humans cannot do without for very long.

Saltwater Supplement 

Even though salt water is a less than ideal form of H2O for human consumption, it is the reason why some people lost at sea have been able to survive on it, rainwater and the odd bit of food for extended periods of time. A pair of fishermen from Kiribati were adrift for 177 days in 1992 before coming ashore in East Samoa, while during World War II, a Chinese man survived aboard a raft for 133 days after the ship he was on was sunk by a torpedo.