Waterfall

What is Waterfall?

Waterfall (waterfall mediation) is a sequential ad serving method that prioritizes ad networks based on historical performance, calling each network in turn until an impression is filled to maximize publisher revenue while ensuring ad space is utilized.

How does Waterfall work?

This traditional approach to ad monetization works by arranging potential ad sources in a predetermined hierarchy based on expected performance. When an ad opportunity becomes available, the system first offers it to the network at the top of the cascade, typically the one with the highest historical CPM (cost per mille). If that network doesn't fill the impression, the opportunity cascades down to the next network in sequence.

While this methodical approach ensures all ad spaces are eventually filled, it can leave money on the table by not allowing lower-ranked networks to compete for premium impressions they might value more highly than the prioritized networks.

How is Waterfall used?

For developers implementing monetization strategies, waterfall mediation offers simplicity and predictability but generally provides less optimization potential than more advanced alternatives like unified auctions that enable simultaneous competition among all potential buyers.