Craig Graham wrote:
troubleinstore wrote:

What was that figure about the number of times London tap water is
likely to have passed through someone before it reaches you?


Eight times and it isn't just London

How's that worked out? Doesn't seem very much if you consider the whole
water cycle and all the people who have ever lived.

Ballpark time.
Say there have been 15 billion people alive.
Urine/sweat/... output maybe 8l/day.
Say 3000l/year of water.

3*10^3l/year/person * 100 years * 15*10^9 people = 4.5*10^15l, or
4.5*10^12 tons, or 4500 cubic kilometers.
The ocean has 1.3 billion cubic kilometers, so well under a hundred
thousandth of the ocean could have passed through a human. (not
one particular human)