Retiring in Barcelona. Living primarily on our own capital from bank accounts overseas.  We have no salary, pension, etc.  Today the health authorities suggested our payments for national health should be based on the amount of deposits from overseas we make annually into Spain. Can they do that?

Sounds pretty fair. After all the money that you’re bringing into the country is the equivalent of what your “salary” might be considered if you were employed here. If the national health care system is going to work it needs to be funded fairly.

IMHO, if you think they can prove your funds via an investigation, then honesty might be necessary. Otherwise you might be able to get away without declaring everything.