To use this shader, you just need to append it from the purchased blend file.
(File/append/... locate the downloaded "poolwater.blend" file. Choose Materials/poolwater)

Its best used with Cycles for  architectural visualization.
But you can use it in EEVEE also! Just be sure to activate "Alpha Hashed" for Blend and Shadow of the Material in the settings tab.
And activate Screenspace reflection, and in its tab activate refraction. 

Eevee wont refract accurate, and the shader wont look like it does in Cycles.

Heres a screenshot in EEVEE:

And heres the same settings in Cycles:

Its the refraction part that introduces some reflection where refraction should occur. But caustics and volumetric density is preserved well of course.