TAKEN WORD FOR WORD FROM
http://sites.google.com/site/aleromo...m-2/air-intake
Bypass Valve
If you're afraid that, with your cold air intake setup, you will inadvertently suck up water and hydrolock your engine, you can purchase the AEM Bypass Valve for peace of mind. What happens is when water begins to suck up the intake piping, the bypass valve opens from sensing the added vacuum, and allows the intake air to be supplied from the engine bay until the cold air intake's filter area is out of water.
Realize that in order to suck up water into your engine, the end of the intake piping must be completely submerged in a pool of water and remain there long enough for it to suck up a massive amount through the piping into the engine. So if you regularly drive through 1.5 feet of water, this is for you.