We have used water injection on airplanes used for crop dusting. We use a 28 gallon tank mounted to the firewall and fill with distilled water. It is good for most of the day (30-40 takeoffs). We don't mix anything with the water and can expect a 50 to 70 degree drop in EGT which is a considerable increase in horsepower. The water increases the air density as if the day was much cooler. According to Honeywell, the engine can handle a little over 100 gallons of water per hour and not flame out. Sure is a kick in the pants for the few seconds it takes to get in the air.
Barryb