Question

The cause of humanity's increased water consumption is an increased population. What is the effect?

Answer 1

As the human population has climbed past seven billion, and the consumption per person of everything from burgers to blue jeans has risen inexorably, the finiteness of Earth’s freshwater is becoming ever more apparent.
It takes water to make everything, and the explosion of demand for all manner of products is draining rivers, shrinking lakes, and depleting aquifers.
Consider this: on average it takes 2,700 liters (713 gallons) to make a cotton shirt and 9,800 liters (2600 gallons) to make a pair of blue jeans.  The cotton crops growing in farmers’ fields consume most of that water; a smaller share is used in the factories that churn out the clothes.
On any given day we’re likely wearing more than 15,000 liters (~4,000 gallons) worth of water.  And if we slip on a pair of leather loafers, well, add another 8,000 liters (~2,100 gallons).  It takes a lot of water to grow the grain to feed the cow whose skin is turned into shoes.
Such figures might not matter if there was abundant water whenever and wherever we needed it – or if water had a substitute.  But water is limited, and there’s no substitute for it.  We need water to quench our thirst, to grow our food, to cool electric power plants, and to make cars, computers and all those cotton shirts.
And that’s why the size of humanity’s water footprint – and of yours and mine – matters.