The concept of the Lazarus Pit has been in existence in DC Comics for nearly 50 years now.
First referenced and seen in Ra's al Ghul's debut appearance back in the 1971 Batman #232 tale Daughter of the Demon, the Lazarus Pit helped to reinvent what readers thought they knew about comic book stories. No longer was death as clinical as was once thought, for now DC had another tool at its disposal for any fallen heroes or villains that they wanted to resurrect.
As we'd come to learn, Ra's discovered his first regenerative chemical pit centuries ago, way before he became the all-powerful, genius-level villain we all know and love. Initially used to save a dying prince, a cruel twist of fate saw al Ghul blamed for the death of his wife and left for dead. Of course, a quick dip in his newly-dubbed Lazarus Pit saw the Head of the Demon back amongst the living and now with a more sinister skew on life.
In the decades since the Lazarus Pits - of which there have been several - came to be, so many DC characters have had to bathe in these mystical waters, with heroes and villains alike having done so over the years.