The Mill's Spillway

A watermill had a channel that directed river water to its wheel.

In heavy rains, the channel could overflow and flood the mill.

So the builder added a spillway — a side channel that opened when the water rose too high, diverting excess back to the river.

"Wasted water," a merchant said. "You could grind more grain."

"I could grind more grain once," the miller replied. "Then I'd have no mill."