Our body is about 70 percent water. Maintaining the body’s water balance is a prime requirement for survival. Water is a higher priority than food. We can probably live for weeks without food (hunger strikers do), but our survival will be measured in days if we have no water. Because the digestion of food drains needed water from our body, we should not eat if we have no water. Every bit of water that we conserve, even perspiration, increases our survival time. While conserving water is vital, so is maintaining enough physical strength to cope with the ordeal of survival. Survival experts recommend that we begin drinking rationed quantities of water soon after boarding a life raft, the amount depending upon how much we have been able to bring aboard. They suggest drinking one half of the daily ration at a time, rather than sipping very small quantities. Thirst may also be reduced by chewing a gum, or practically anything else. However, this relief does not reduce the body’s need for water. Drinking seawater will exaggerate thirst, promote water loss through the kidneys and intestines, and shorten our survival time.
Anyone who has accidentally swallowed a mouthfull of seawater may imagine that drinking glasses of it would be impossible potentially dangerous and lead to kidney failure. They would be correct, sea water is about 3 times as salty as human blood, normally the the fluid in body cells is about the same saltiness as the blood, but if we drink seawater the less salty water in the cells will flow out through the cell walls into the saltier blood. This causes the cells to shrink and malfunction, resulting in weak aching muscles and an irregular heart beat a loss of concentration and mental function. The bloods high concentration of salt causes the kidneys to get rid of the excess by producing more urine, so drinking seawater not only fails to provide fluid the body can use but also causes the body to lose fluid it is already using.
Dr Bombard said that he drifted for 63 days on a raft "without any food and water other than that which the ocean provided" and on the basis of this he recommends not drinking more than about a litre a day of seawater, as he says he got sick if he drank more than this. But Bombard was not just drinking seawater he was eating fish & drinking rainwater (which the ocean provided), and the fluids in most fish are ok to drink.
IN SHORT DRINKING SEAWATER IS ONLY RECOMMENDED IN A SURVIVAL SITUATION AND ONLY AS A SUPPLEMENT TO DRINKABLE WATER FROM FISH OR RAIN OR TO EAK OUT A REMAINING FRESH WATER SUPPLY.
IT IS NOT GOOD FOR THE LONG TERM HEALTH OF YOUR BODY.
BECAUSE DRINKING SEAWATER INITIALY RELIEVES YOUR THIRST IT IS IMPORTANT NOT TO DRINK TOO MUCH.
LESS THAN A LITRE OF WATER A DAY MEANS HARD PHYSICAL EXERTION IS OUT OF THE QUESTION ... Robert

  photos corbis.com & Alain Julien/AFP
Bruno Vogin, 36, and his monkey Mouguie left the Cape Verde Islands on January 9th 2002 in a liferaft to try to emulate the experiment in ocean survival of Alain Bombard. Bruno hoped to reach the West Indies in 2 to 4 months after a voyage of around 4500km.
Bruno and Mouguie were reported missing off Brazil on April 7th 2002. Their boat was found empty off the coast of Amapa. The last radio contact with the maritime surveillance authorities was on March 5th 2002. The day before, an Italian sailing boat brought drugs to Bruno to treat infected wounds on his legs.
("Drinking alcohol under the conditions of lack of water is suicidal")

DR BOMBARD DID NOT SAY HE DRANK ONLY SEAWATER, HE HAS BEEN WIDELY MISQUOTED ...