Use a spillover to create a pool window.
Note: This guide applies to Pool Studio and Vip3D.
To add a pool window, begin in the Pool Stage. There, add a Spillover to your pool and turn off Water Flow:

Next, go to the Materials Stage. Double-click the spillover and apply glass from the Library:
Go in the pool to apply glass to the inside of the spillover as well:
Finally, add a custom shape that is the same width as the pool beam for the bottom. Use the Outline Tool to trace the outside pool line and then press the large orange endpoint to set the width to 1 ft:
Check out your finished work in 3D: