A wa­ter­mark is a no­tice (e.g., “Draft”, “Con­fi­den­tial”) that’s printed in the back­ground of a page. Of­ten in six-inch let­ters. Di­ag­o­nally. In red.

Wa­ter­marks in­ter­act poorly with the text, cre­at­ing vi­sual noise that dis­tracts from read­ing. (It’s a vari­a­tion of the prob­lem noted in rules and bor­ders.) Also, wa­ter­marks can darken con­sid­er­ably when pho­to­copied, ag­gra­vat­ing the problem.

It’s hard to make wa­ter­marks look good. Bet­ter to con­vert the wa­ter­mark to a no­tice within the header or footer.