People are not that stupid to be told that they need to drink water. Our bodies tell us when we need to drink - we simply become firsty. Sometimes we need more (like during certain prolonged atheltic performance or in very hot environment due to extensive sweating), sometimes less. The 2 litre a day is bullshit. 160cm tall female with 60kg body weight living in arctic circle may need only 0.5 litre of water a day. 2m tall male lumberjack weighing 120kg, working in tropical forest may need 6 litres a day. And so on...
It becomes stupid when we perpetuate and follow myths.