Artbrooks, someone once estimated that the water in the carafes in the House of Lords, England's upper parliament, had been through 12 sets of kidneys before it got there.
Most of them not human.
No idea how they worked it out.


Of course, there is no 'new' water. The same water has been around since the earth cooled, recycling over and over, so the water has been through BILLIONS of kidneys.
Hope this is a comfort to someone.