Spain has about 2.2 trillion euros of bank deposits, and about 560 euros of bank bondholders. I've estimated the spanish banks will need about 550 billion in new capital to replace the losses from their property bubble once everything is said and done. Bubble losses stem from two areas - corporate debt gone bad, and homeowners who can no longer pay their mortgages. You can see in the Loans vs Property Prices chart below, that corporate loans have defaulted quite a bit more violently than those from the homeowners. Yet both debt levels must drop down much closer to their starting points than they have done to date. And it is all led by property prices - which have yet to retrace back to their origin, as is usual in a bubble pop. That's where the banking losses come from; loans being written down, stemming from the dropping value of property.
When a bank has losses that push its assets below its liabilities, the bank must be "resolved" - i.e. it goes bankrupt. At that time, the losses are apportioned to people who have lent money to the bank. This includes depositors, as well as bondholders. You can see by the following chart that Spain has about 560 billion in bondholders, and about 1.6 trillion in deposits. In truth, there are about 2.2 trillion in deposits in Spanish banks, but other groups have been eliminated to keep the chart simple. Where will the losses in Spain fall? Uninsured depositors? Or bondholders? Or some combination of both? Is Cyprus really the new template?
You can see that depositors really haven't started to flee Spain at all, except perhaps the eurozone MFI group. Something to watch.