Well, no one said there is a downside - maybe there is, we simply don't know. Just like we do not know whether drinking two liters of water does have any benefit at all.

Recently, I have read an article which claimed that one should only drink water when their body demands it, you know, like becoming thirsty. The problem is, in most of the popular science circles these kinds of urban myths are propagated almost as if they were basic nutritional facts. I would personally think some mega-companies, such as Nestle, would be really interested in propagating the myth of the necessity of consuming at least two liters of water.

also, you might be interested in researching why cutting back saturated fats might not be as beneficial as it has been claimed for decades now. Actually, there is a new kid in town - ketogenetic diet.