Does a water to gas product void my warranty?
No!
The Federal Magnuson-Moss Warranty Act of 1975 states:
  The vehicle manufacturer cannot void the warranty on a vehicle due to an aftermarket part or procedure unless they can prove that said part caused or contributed to the failure in the vehicle.

The Federal Magnuson-Moss Warranty Act of 1975 (15 U.S.C. § 2301) prohibits any vendor that gives a warranty to its customers from taking away that warranty by making any claims against the customer that it cannot support.
The vendor must be prepared to demonstrate or prove that in some way the customer did damage the vehicle or warranty product with an aftermarket device.

Claims or threats cannot be directed to a customer simply because the vendor disagrees with the customer.

You can find further information at: http://ftc.gov/ogc/stat3.shtm, or http://www.law.cornell.edu/uscode/15/ch50.html

This information can be found at http://www.brightgreen.us/faq.htm

While our research continues; to date, we have found no problems with any water-to-fuel conversions.
There are special requirements for pure hydrogen and hydrogen-from-water systems that do not include petrolium fuel mixes.
With water-to-fuel conversions, the exhaust system would need to be stainless steel if no petrolium fuel was added.
With pure hydrogen, it is doubtful that you would want to take on the many alterations needed to perform this specific conversion!