Chris is right the tax is called Patrimonio is levied on all your assets reduced by mortgage etc.
Notional Rental Income and not allowing expenses against rent is another Spanish Goverment ripping of non Spanish residents.
I am dissapointed that the latest change in CGT would have been a good time to look into this inequality. However in a Country which likes to bite the hands that feed it. I am not surprised that this has not been done.
What is silly is that while the Council can takes years to establish the cadasteral value the tax is due and yes you guessed it intrest and penalty along with it