IMPORTANT: This shader is only for Blender 2.81 and newer

AWS is the ultimate shader for rendering realistic natural water in still scenes 

What you get:

-AWS-Volumetric Shader: use when big and/or important objects are in the water and a realistic underwater falloff is required. Requires a high amount of transmission samples

-AWS-Performance Shader: use when underwater falloff is not required and/or decreasing render times is important. Also use this one when rendering in Eevee

FAQ:

Q= How do I start using this shader?

A= Download the attached .blend file and save it in a location of your choice. In the file you wish to use the shader, go to file>append and locate the AWS blend file. When selecting the file you will be presented with a menu structure, go to the materials folder. Here you will find the two shaders.

Q= I am not seeing the underwater color when using the AWS-Volumetric shader

A= This means your volumetric samples are set as 0, change this to 1. You will find this in the Render tab under the Light Paths menu

Q= All the reflections in the water are blurry

A= This means you either have very high waves (which realistically cause blurry reflections) or the Long Exposure slider is not set to 0

Q= I am not seeing the underwater color in Eevee

A= Please make sure the Eevee/Cycles slider is set to 1

Q= The Performance Shader is barely reflective when rendering in Cycles

A= Please make sure the Eevee/Cycles slider is set to 2

Q= I am using the AWS-Volumetric shader, but I can't see anything under the water surface

A= Make sure the mesh your shader is applied is solid (so not a plane) and itdoesn't have any holes, it needs to be a closed shape. If this doesn't work, make sure your murkyness slider is not set too high.

Support: 

Because of the complexity of the node setup, please do not refrain from reaching out with questions or suggestions

Credits:

Video music: Soulstone by Audionatix licensed under CC BY 3.0, listen here: https://www.youtube.com/watch?v=MyyMXafoL-A

The shader uses a node trick for making an advanced Color ramp by using math nodes. This trick was invented by PGMath and shared on the Blender Stackexchange