Dear Sir/Madam,

What you are committing is Fiscal fraud and can be charged for it if the Spanish Tax Authorities find out or if someone reports you to them. Articles 305-310 of the Spanish Criminal Code.

It is mandatory to declare all your income here in Spain and pay all the associated taxes providing you are a fiscal resident in Spain (spend more than 183 days a year in Spain) which is your case.

Besides the above, as you own property in Spain you are additionally liable to pay Wealth & Income tax, IBI and garbage collection.

Wealth tax has now been abolished but you still have to file and submit it for "control purposes".