Yes, you can, but the quality will vary. Regular or more finely ground coffee will result in more thick coffee sludge in your cold brew rather than a clean, clear liquid. If you go this route, take the time to strain the cold brew through a filter 1-2 extra times to help get rid of some of the sludge. It will also brew more quickly, so don't let it go more than 18 hours or it could turn bitter.