well it

 

Headgasket.

I wouldn't try starting the car again, if you get too much water in there you'll bend a rod!

 

Most likely head gasket, AFAIK the water in the turbo does not have any path that it can take to get into the air flow path, it's sort of in a jacket around the bearings.

And if the head gasket is intact around the oil passeges but failed at one of the water passages, there's not much chance you'll get water in the oil.

 

[m A

 

If you have water in the bore, the compression effect will mash your rods

 

rub

 

You either have a failed head gasket,allowing the coolant to get into the cylinder and then out the exhaust.Take the spark plugs out and spin the engine over - you will see the water pumping out the spark plug hole on the cylinder where the gasket has failed.
Or you might have an Internal crack on one of the cylinder heads,allowing coolant into the exhaust ports.
Either way you dont want to run/start it with a lot of coolant in the cylinder as jay m A said - you cant compress water,and you will bend a con rod.
Time for an engine tear-down to see what has failed.
Early WRX's use a Composite head gasket,so might be worth uprating the gaskets to the STi Version 3+4 MLS gaskets.

Mick

 

site