It will not just be water. I cannot remember if the Subaru stuff is a mix including water, but when i had mine changed years ago, i use the Silkolene ProCool now and always have done since. This once in the system, is not diluted and you just poor it in from the bottle. But you will need to fill the whole system with it.

 

Anti-freeze

 

Anti freeze. I bought a bottle from the local subaru dealer. IIRC it's ethylenglycole based so you can use any ethylenglycole based antifreeze.

 

Step away from the vehicle, put down the spanner, and do yourself a favour by ringing you local specialist and getting them to do whatever you are attempting