Water 

The ability to provide clean drinking water is a cornerstone of human civilization. Yet, moving portable water has always been an engineering challenge. In Tenochitilan, Aztec engineers designed a two-channel aqueduct that transported water nearly three miles from natural springs to the island city. The twin-tubed system allowed water to continue even when one channel was being maintained, never interrupting the flow of water. For centuries, civil engineers have helped bring this life sustaining resource to people.