Here's why:

* Refractive Index: The speed of light in a medium is determined by its refractive index. A higher refractive index means light travels slower in that medium.

* Water vs. Glass: Water has a refractive index of approximately 1.33, while glass has a refractive index ranging from 1.5 to 1.9 depending on the type of glass.

* Conclusion: Since glass has a higher refractive index than water, light travels *slower* through glass than it does through water.