Here is a description directly from their informational page, about just how safe it is to use water as fuel for your vehicle.
The process is very safe because the combustible gas is extracted as needed and burned steadily from the water, unlike larger volumes of pure hydrogen which are highly flammable.
WHY COMPRESS HYDROGEN IN DANGEROUS HIGH-PRESSURE TANKS WHEN IT IS ALREADY "COMPRESSED" IN PLAIN WATER - AND CAN BE EASILY AND SAFELY RELEASED??!
Our set-up produces hydrogen as your car needs it, rather than using storage tanks. Thousands of cars have been safely converted without any issues or incidents.
Best of all, this conversion process is completely reversible so it will not void your auto manufacturers warranty. It simply acts as an add-on to significantly increase your fuel efficiency.
Experts Agree: Water is a Viable Fuel Technology
I think the best thing about the process would be that it doesn't void your warranty, and that the effects are reversible. That way if you don't like the way things turn out, or you just don't feel comfortable with the results, you can change everything back to the way it was.
So check out the site: runyourcaronwater and purchase their dirt cheap guide if you are interested.