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Just had a look at the coolant tank thing and noticed that there was no coolant. What is the correct coolant for a 1996 Toyota caldina? And will putting just water in the expansion tank be ok for now?

Yes, you can top up with water in the mean time. Someone like Repco will be able to sell you the correct coolant for your car. However, more importantly, you need to find out why the coolant level is low. The cooling system should not lose coolant, so if the level is low it either has an external leak or is losing it through the engine somewhere, which can potentially be a more serious problem.
If you can't find any evidence of a leak that you can easily fix, I'd suggest having a mechanic carry out the appropriate checks (Tee kay and pressure tests).