How? The only option I have is to make it washed out or not.

On a page showing the watermark, select and copy it. It will be in the header.

Then remove the watermark.

Then go into the header and paste the watermark image back.
Right click on it and adjust the transparency.

Note that anything in a header or footer will appear washed out when you are viewing the document on screen. Does your watermark appear the way you want when you print?