8 regular sized tumbler's is a good indication of how much to drink, but if you drink plenty of tea, coffee and squash your 6 glasses will be plenty, your normal every day drinks should be part of your daily allowance, but I drink a 2litre bottle of sparkling water extra to my normal drinks, just because I love drinking water and have done so for many years.
It's not only good for your diet, but it helps your skin stay nice and soft too by keeping it hydrated, if your skin dry's out, that's when wrinkles start forming, it also keeps our kidneys working properly too, so water is very good for us - all of the time.