I've found that most pumps that say they are made specifically for terrariums are overpriced and weak. The Aqua Lifter Vacuum Pump AW-20 probably wouldn't be what you want since its only a few gallons per hour. That's more of a drip than a waterfall. For my tank I bought a 200 GPH pump from Lowes in the pond section. I'm sure it would have no problem elevating the water to 20 inches.