Air-side economization uses outside air for cooling, while water-side economization uses a heat exchanger to transfer heat from the data center to the outdoor environment. Air-side economization is often simpler and less expensive to implement, but may not be effective in hot and humid climates. Water-side economization, on the other hand, can provide more consistent cooling performance, but requires a larger upfront investment. Both strategies can be effective in reducing cooling energy consumption, but the choice between them depends on the specific climate and data center requirements.