The former lovers dined at Gjelina, a restaurant in Venice, California, reported Ace Showbiz.
According to an onlooker, there wasn't something romantic during the dinner. The film stars then left the venue together in the same ride.
Cooper, 40, and 23-year-old Waterhouse began dating back in 2013, but it was not until the following year that they made their first outing as a couple when he brought her as his date to the 2014 SAG Awards.
They then appeared together again at a White House state dinner in February the same year.