Huh. So, when Reepicheep in Prince Caspian discovers that the ocean is no longer salty but tastes sweet, we can rule out that the oceans of the far reaches of

Huh. So, when Reepicheep in Prince Caspian discovers that the ocean is no longer salty but tastes sweet, we can rule out that the oceans of the far reaches of the world containing Narnia are made of heavy water, because if it were then he wouldn't have been able to taste it. Though I suppose any fan theory in this direction could be salvaged by the conjecture that talking mice are different.