Personally, I would never run any kind of additive injection (meth,water, nitrous) without a stand alone ECU capable of drastically changing the tune if it detects you've run out of juice. These things break or run out when you're not expecting and without a fancy system to protect your motor, it's a time bomb. The Hydra does this type of thing but most of us don't want to deal with a non-ODBII friendly EM or the huge pricetag and tuning know-how requirements.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD