75% alcohol disinfection does not need to be mixed with water, because the alcohol used in medicine is basically 75% concentration of alcohol, which is currently recognized as effective in killing pathogenic microorganisms including bacteria and viruses on the surface of the object or skin, and does not produce irritation to the human skin mucosa, respiratory or digestive tract mucosa. If mixed with water, the concentration will be low. Less than 75% of alcohol will not be very effective in killing pathogenic microorganisms, because the concentration is not enough to play a significant role in the elimination, but in the use of the process brings harm, mistakenly believe that has been killed, but in fact did not kill, it will lead to the spread of infection.