Hi,
Wealth tax is calculated from the valuation of your property/mortgage. Your mortgage provider issues a certificate showing exact figures around the start of each financial year. The wealth tax is calculated from this. The tax itself is payable in December.
Most solicitors will act as your fiscal representative to the tax authorities for a small annual fee and will sort everything out for you.
I have been told to expect anything from 300 to 600 euros for a £120000 property.