Refactoring the design was mandatory to meet statutory emission and fuel consumption limits. Moving to water cooling, reducing aerodynamic drag and using lightweight materials were all necessitated by this.

There's a DVD called "The Porsche Way" available at the Porsche Museum in Zuffenhausen in which F.A. Porsche himself defends the move to water cooling, justifying it with legislation.

As it is, Porsche already has to pay CAFE penalties in the US, and similar legislation exists in the EU as well, called Flottenverbrauch.