After I wrote the last post, I did some Google search (I was about to say "googling", can I?) and found this article which actually described how to make a water-injection system for as little as $3.72.
If it did not work, you can always revert back to your car's original configuration. Why not give it a go, or at least you can have fun tuning your car for an afternoon. If it works (and I believe strongly that will because I had a similar system long time ago), your $3.72 investment will have many times pay back.
I am going to try this myself in my next available free afternoon.