eli5 Is there a reason the waste water like from showers can’t be filtered through pipes and used for toilet water?

Question

eli5 Is there a reason the waste water like from showers can’t be filtered through pipes and used for toilet water?

In: 797

Answer 1

It can be. However, with showers you would have to store it. Instead, you can put a sink above the cistern, wash your hands then have it autoflush with the used water.

And surprisingly, these exist