We are not in 70's anymore. I would strongly recommend foreigners planning to buy a house in Spain not to take this for granted and to consult the current law first in https://www.boe.es.

You "can build in the middle of a dry riverbed" (if nobody is watching) is not the same as "you will be allowed to repair" when your house will be flooded six years later. (And it will happen, because this place was called 'las ramblas' for something).

The real state promoter wants your money, not your friendship, so using the services of a professional consultant can save you a lot of future headaches.