I find most adverts for 'health' products irritating and also often misleading. However, whilst the current volvic campaign is undoubtedly annoying, for once I agree with the message. Drinking water is good for you and most people aren't drinking enough.
But what has this got to do with weight loss?
Well water is one of the inputs into the chemical reaction in your cells that produces energy. Therefore if you are dehydrated you won't produce as much energy in your cells and will therefore burn less calories. The relationship isn't linear - it is possible to drink too much water - but 1.5 litres per day as per the volvic challenge, is a reasonable amount.
Hunger can also be thirst in disguise - the body may crave food for it's water content if you are dehydrated. Therefore if you find yourself reaching for a snack it's a good idea to have a cup of water or herbal tea, wait 15 minutes, and see if you are still hungry before you eat, and you may end up eating less. For the same reason it's a good idea to avoid diuretics such as caffeine and alcohol.
There are other benefits of drinking water too, dehydration can lead to poor concentration, poor sports performance and dry skin, and water also helps detoxification by the liver.
So if you want to lose weight and are not drinking enough water, in the strange words of Jimmy from the volvic ad, maybe 'give it a bash'!