Total internal reflection is possible when light travels from

Total internal reflection (TIR) can only take place when two conditions are met:Light travels from an optically denser medium to an optically rarer medium.The angle of incidence exceeds the critical angle.Comparing refractive indices (${\mu }_{\text{glass}}>{\mu }_{\text{water}}>{\mu }_{\text{air}}$), the only path here going from denser to rarer is from glass to water.