Most authorities say you should drink at least 64 oz (approx. 2 litres) of water per day, and it is suggested that you drink an additional 8 oz (approx. 250 ml) for every 25 pounds (approx. 11.5 kg) over your ideal weight. During hot weather, and any physically strenuous activity, you should drink even more.
As Donald Robertson, an American doctor, explains:
"Studies have shown that a decrease in water intake will cause fat deposits to increase, while an increase in water intake can actually reduce fat deposits. This is because the kidneys can't function properly without enough water. When they don't work to capacity, some of their load is dumped onto the liver. One of the liver's primary functions is to metabolise stored fat into usable energy for the body. But, if the liver has to do some of the kidney's work, it can't operate at full throttle. As a result, it metabolises less fat, more fat remains stored in the body and weight loss stops.
Drinking enough water is the best treatment for fluid retention. When the body gets less water it perceives this as a threat to survival, and begins to hold onto every drop. Diuretics offer a temporary solution at best. They force out stored water along with some essential nutrients. Again, the body perceives a threat and will replace the lost water at the first opportunity. The best way to overcome the problem of water retention is to give your body what it needs - more water. Only then will stored water be released. The overweight person needs more water than the thin one.
Water helps maintain proper muscle tone. It does this by giving muscles their natural ability to contract and by preventing dehydration. It also helps prevent the sagging skin that usually follows weight loss.
During weight loss, the body has a lot more waste to get rid of - all that metabolised fat must be shed. Again, adequate water helps flush out the waste.
When the body gets too little water, it siphons what it needs from internal sources. The colon is one primary source. This can result in constipation, which is normally alleviated when enough water is drunk."