If you are the owner of a Spanish property, but not registered to pay Spanish income tax, you must pay a non-resident tax. This is paid to Hacienda (the national Spanish tax office) on an annual basis, via Form 210, and it must be paid prior to December 31st of each year.

Late payment can result in fines and so it is a good idea to leave this in the hands of a tax professional, who will also be up to date with the seemingly ever changing amendments to the fiscal laws.