It has become a certain belief among the public-drink at least eight glasses of water a day to improve health and well--being.Bottled water companies often repeat it to increase their sales but it is actually a silly idea. There is no evidence to prove the advantages of drinking eight glasses of water a day,scientists say. The misunderstanding is caused from the suggestion that adults should drink 2.5 liters of water daily,which was highlighted(,)by the British Medical Journal in December.The important part of the suggestion that most of this quantity of water is contained in prepared foods,however,is usually ignored.     U.S.researchers who reviewed the evidence concluded that most people do not need to worry about the amount of water they drink every day.Besides drinking water,they will be getting plenty of liquid in other ways.Caffeinated drinks such as tea,coffee and cola,and alcohol  can help reach the daily total if they don't drink too much,though these drinks help the production of urine . Less well known are the dangers of drinking too much water,causing water poisoning,low salt levels and even death.     The review of research by Dan Negoianu,from the University of Pennsylvania,found that not a single study included the suggestion of drinking eight glasses of water a day.Although one small study suggested that drinking water could result in fewer headaches,the results were not very important.However,the benefits of drinking some water to prevent a pain in head after drinking too much alcohol are.separately,proved to be true.     No studies showed any advantages to the color1 of the skin because of the increased water taken into bodies.Dehydration can make skin less pleasant,but there was no clear evidence to support the idea that water helps people keep a youthful appearance.The researchers also found no evidence that drinking lots of water does some good to the body's organs . The writer's main purpose of writing this passage is to  _  .
persuade people to drink different kinds of water warn people of the danger of drinking much water tell people drinking much water is not as healthy as is considered help people realize the importance of drinking enough water every day