Why infra red spectroscopy would not be able to detect the presence of water in a sample of ethanol

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In both compounds, the most prominent absorption is due to the bridged O-H stretch vibration - while ethanol in water could be detected due to the C-H stretch absorption, the other way round doen't work as water possesses no clear vibrational bands that are not present in ethanol. For ethanol spectrum, see

http://riodb01.ibase.aist.go.jp/sdbs/cgi…

and for a spectrum of water see

http://www.brandon-russell.org/images/na…