Originally Posted by DanJ
...Maybe the rules have changed since then.
Go back and read what I wrote earlier. It depends upon aircraft type, distance and passenger load.
A320 YOW-YUL can likely go without any lavs working
A320 YYZ-YEG can likely have 1 lav in-op with a 75% load
A320 YUL-YVR probably has to have all of them functioning regardless of load.
A Dash might be able to fly any place without a lav. In each case you have to check the manual.