Shadergraph: How to amplify all of the white color of a texture?

I have a shader for a waterfall which uses a noise texture and I constantly modofy the offset to give the effect of flowing water. I also added some transparency to shadergraph. I am using this texture.
173324-ef-waterfall02-alb.png

How would I amplify all of the white color of the texture, but not the black? I tried putting an add node with a white color, but that just “amplified” the whole texture. I want to do what that add node did, but only for the white areas of the texture.

Have you tried using Simple Noise?

Take a look at the example I made: