NHRA doesn't want the turbo cars using water injection because: 1. It's just one more thing for them to have to "police," and 2. Water injection would allow the turbo cars to run a LOT more spark advance, which translates into a significant "boost" in power (no pun intended.)
They (NHRA) just went through a lot of grief, slowing the Pro Mod turbos down; they don't want to have to do it all again, particularly, not so soon...
Buddy Ingersoll's impressive turbocharged Pinto was never allowed a drop of water (injection) by the NHRA. It's just a detonation-prevention gimmick that works.
The more things change, the more they stay the same...