Coolant leak

My 2000 Blazer has a significant coolant leak on the front drivers side of the engine. I add water, half a gallon runs out. Freeze plug? Intake gasket? Could the intake gasket leak so quickly? Help?

Welcome to AF.
You need to have a look and see where it is leaking.

It may help to remove air compressor and bracket to see it real good.
Check for intake leakage and water pump and freexe plug and kead gasket leakage.
Let us know what you find or see.

Go to AutoZone and borrow the Radiator Pressure tester. It is a small hand held tire pump with a Radiator cap on it. When the engine is cool, and shut off, Attach the tester to the Radiator and pump it up to the pressure rating of the Radiator Cap. Your leak should be very obvious to see.

Not to be a stickler for details, but you mentioned pouring water in to replenish the coolant. Make sure you're using a 50/50 mix. I understand if you use water to find the leak (distilled or deionized), but make sure you bring it back to the proper ratio with full strength coolant.