Water

Water is the CoD term for the rare magical substance known as http://castle-clash.wikia.com/wiki/Mana in Castle Clash.

Players can Trade Water for items in the Warehouse at very attractive rates. (Trade only 60k active water for 300k bottled water, etc.)

A level 18 Reservoir apparently holds slightly more water than an https://en.wikipedia.org/wiki/Olympic-size_swimming_pool does.

A level 25 reservoir holds 1.4 million gallons of water in a 3x3 (x3?) space and appears to be the largest possible sphere that can fit inside that cube. If so then each building space in the game is 24 American feet long. Which means that Swordsmen are sprinting as fast as Usain Bolt.