Ok, this makes it a little clearer, but past choices have future consequences. So (implicit) choices made for 2018 will now carry over to 2019.
You may be familiar with the different 'boxes' within the Dutch income tax system:
- box 1 taxes income from work and home (37-50%)
- box 2 taxes mainly dividends (26,5%)
- box 3 taxes savings and investments (30%)
With the 30% ruling you get the 30% tax free in box 1, but are treated as a normal resident otherwise in box 1. But at the same time you are treated as a NON-resident for income in box 2 and box 3, which means you do not declare those sources of income in the Netherlands.
Now with regard to your bank and/or savings account, it either falls in box 1 (if you want it to be a business asset), or it falls in box 3 (if you want it to be a private asset). From your answers, I gather that you did not declare the savings and bank account in box 1 (you didn't declare them as business assets), which automatically means you implicitly declared them in box 3 as private assets. Where they remain untaxed in you declare yourself a partial non-resident taxpayer, as far as I understand, because of the exemption for foreign assets.
However, it is a question if the bank and/or savings account qualify as foreign or non-Dutch sourced income assets though. I simply don't know that. But even if you don't declare partial non-residency for box 3 and the bank and savings account are declared in box 3 as private assets, you don't pay taxes if they don't exceed some 60-odd thousand euro for couples filing jointly. That's the regular exemption for residents anyway.
Because of this choice in 2018, you cannot change it in 2019. This means you must keep the bank and savings accounts as a private asset. As a result, you probably should not declare the value of the bank account in your balance sheet (in box 1) at all, but only in box 3.