Both the Source and the Triad are refer to as the highest hierarchy in the reign of evil.
In many episodes, when the front door of the manor is opened in an exterior shot there is clearly a solid wall behind it, however in the sets there is a long corridor behind the door.
in several cases throughout the series the view seen through the attic window is inconsistent with the houses location (possibly the studio grounds).
In several episodes (mostly from season 5 onward), you can see ceiling segments missing from the manor when low angle shots are used. The ceiling panels are in large square, sometimes rectangular segments that are able to be removed to position studio lights for certain shoots. In many scenes these are missing, revealing the open studio space above the set.
In several episodes, when the sisters are baking a pie, it is clearly visible that the pie crust is empty, even though the person baking the pie has poured in the filling earlier.
Throughout the series, stock aerial footage of San Francisco is used. The footage often contains the Embarcadero Freeway (I-480/CA-480) a structure that used to run along the San Francisco Bay north of the Bay Bridge. The structure was removed in 1991, a full seven years before the series started.
Age difference between the sisters is not constant. In season 8, Piper says Prue was 5 and she was 3 when Patty was pregnant with Phoebe. In season 3 however, Prue says Piper was 1 and she was 3 when Phoebe was born. And many other contradictions that are too long to list.