Yes, in Spain there are very strict sanitary laws regarding dairy milk or any other farm produce, and the requirements are probably just as tight as those in the US. About any earthworks, buildings and the like, before you start doing anything on your plot of land you must have a
project signed and endorsed by an Architect/Engineer, and any waterworks scheme or whatever you do must be in the project and must fit into the municipal urbanist plan. Otherwise, you'll never get the permits to build anything. If you decide to present a passable project and later make unauthorized changes, there are very high chances your neighbors are going to report the authorities and apart from receiving a fine, you'll need to undo what you did.
Spain is divided in autonomous communities, who in some areas have exclusive competences, so some things may vary from region to region. So in addition to nation-wide and municipal laws, you must accomplish the regional ones, who may be stricter. A common saying here in Spain is that "we pay Swedish taxes and receive African services", and even if the African part it's an exaggeration, the Swedish part regarding taxes and regulations is not.
I'm Spanish, and I wouldn't buy land in Spain. As far as I could compare, land in a decent location (not in a heavily-depressed area, I mean) it's pretty expensive, at least compared to land in the US. I think with a bit of effort and savings I could definitely buy some decent piece of land in the US; in Spain, I
should win the lottery to get one. Sorry to be that harsh, I'd hope I was wrong. Anyway, welcome here, have a good time!