[gumby79]

Having to buy "clean "distilled watter is a major contributor to the OEM's are not using water injection. Most customers would just fill from the tap causing the system to be prone to failure and a warranty nightmare. 10% rule would render the device useless.
In the Army we had the 10% rule .
It states, You must be 10% smarter than the device you are trying to operate, in order to succeed at operating it.

Will you be injecting before or after the turbo? After the IC is my recommendation, to prevent water condensingin the IC causing a restriction or worse a sudden surge of unmetered water.

Onbord distillery. That'll do maby use a trans cooler to condense the water. So that you can have an air gap. . Insulate the pressure vessel. Be prepared for sudden presure spiks as you hit bumps and turn,stop, start causing the water to slosh onto the hot dry parts of the boiler.
Maby a small boiling chamber( like an egr cooler) with a suplly tank . To keep all of the boiler internal surfaces wet like a house boiler/Hydronic systom.

This is a very informative site
https://www.rbracing-rsr.com/waterinjection.html