The Porsche 911 generation that first used a water-cooled engine was the 996.
Introduced in 1997 for the 1998 model year, the Type 996 replaced the 993 and marked a major technical break with Porsche’s long-running air-cooled 911 tradition. Its naturally aspirated flat-six used liquid cooling, helping Porsche meet increasingly strict emissions requirements and extract more performance from the engine.
The change was controversial among enthusiasts because every previous production 911 had used air cooling for roughly 34 years. The 996 also shared development work and several components with the 986 Boxster, including parts of its engine architecture, suspension, and interior. That common engineering helped Porsche reduce development costs during a financially difficult period.
A common mix-up is the 993, which was the final air-cooled 911 generation, not the first water-cooled one. The later 997, introduced after the 996, continued the water-cooled layout.