How much water is enough?

Introduction

We ALL know that water is essential for sustaining life. But how much water is enough? The answer, surprisingly, is much less than we think. Researchers say it is not the quantity but concentration that matters. Life needs "biologically available" water, which scientists call water activity. If pure water, which represents maximum water activity, has the arbitrary value of one, organisms can get by at 0.6 water activity.

Source

Down to Earth December, 2014