Answer
$\approx 5\times10^4 L$.
Work Step by Step
A rule of thumb says you should drink eight cups of water, or about 2 liters of water, each day. Assuming a lifespan of 70 years, and rounding off to one significant figure at the end, we find the approximate amount of water consumed as:
$$(70 years)\times\frac{365 days}{year}\times\frac{2L}{day}\approx 5\times10^4 L$$
