I have ran water injection on previous cars and the big issue was always keeping the water flow metered correctly. I was browsing around looking at unrelated stuff and came across this pump. It should be here today so I will try hooking something up this weekend.
Peristaltic Liquid Pump
It is 12V and 300mA max current. Flow rate: up to 100 mL/min.
It has a low enough flow rate that I am hoping I can just run it in parallel with the tbi injector in the car and have it pretty close to the right gas/water ratio. My plans are to hook this pump up and plumb it into the throttle body in an unused vacuum port. I will put a gallon of water in the car with 1/10 gallon divisions so I can adjust it by putting a resistor in series with the motor until I get the ratio of 10 gallons of gas to 1 gallon of water.
If it works out the injector PWM signal should give me proportional water flow and after getting the speed right I can just change over to a larger water tank and have a pretty reliable system that will finally meter the water properly. It would be a pretty easy system to duplicate and get working on just about any car.