Why are water storage tanks usually built on towers or hilltops? ?

Because when you open the faucet, you want the water to
rush out with pressure, not just dribble or ooze out.  The
water has to be supplied to the user with pressure.  Either
you supply it from a height, or else you'll need to use pumps
to make the pressure.

The chemical reactions lab we did is typically called a "copper plating lab,  because the acid solution cleaned the pennies and made the copper look shinier;   the acid solution cleaned the paperclips and made them look like pennies;   &   the copper from the pennies was removed, and then added to the paperclips.