Nib asked, and Nib — askNib's tutor — drew the answer live at a whiteboard. This is the spoken transcript; enable JavaScript to watch it drawn.
how do skyscrapers get water to the top
Turn a tap on the hundredth floor and water just comes out. Yet the city's pipe under the street can only push it up a few floors.
Nobody sucks it up, either. Air pushing on the water below does the lifting, and one atmosphere holds up only about ten metres. So pumps sit low and push.
Pushing has its own problem: weight. Every foot of water adds point four three three pounds per square inch at the bottom, so pressure climbs as a straight line.
A column as tall as the Burj Khalifa, 2,722 feet, would crush its bottom pipes with about 1,180 psi. Code caps a tap at 80 psi, the weight of just 185 feet.
So towers climb in stages. Pumps lift water to a tank partway up, more pumps lift it to the next, and each stretch feels only its own weight.
The Burj Khalifa does it with seven two-storey mechanical floors, and delivers just under 250,000 gallons a day. Below each tank, gravity feeds the floors.
A skyscraper's water never makes one giant leap: it is passed up from tank to tank, each pump lifting only a small slice of the height.