The Christmas edition of the British Medical Journal usually has a series of light-hearted articles in it. Last month's copy was no exception. In one of the articles, entitled "Medical myths" (Vreeman & Carroll 2007), the authors wrote "We generated a list of common medical or medicine related beliefs espoused by physicians and the general public, based on statements we had heard endorsed on multiple occasions and thought were true or might be true. We selected seven for critical review". The first myth critiqued was "People should drink at least eight glasses of water a day". Searches on Medline and Google apparently yielded no hard evidence supporting this advice. There are many sources stating that it's good health practice, but they could find no worthwhile evidence to back it up.