Poor Man's Nitrous--Water Injection

I was wondering how effective a water injection system would be. A water injection system, I believe, is similar to nitrous today in that it sprays water into the intake airstream of the engine, and apparently was effective, as I've gotten ahold of a 1959 issue of Popular Mechanics and read an article in it about midget pylon racing. In which, water injection systems are prohibited. It must be quite potent to be forbidden in any racing event that does not require stock parts. Has anyone heard of such a system, and may have any clue to how effective it is and its advantages/caveats?