Exemption from Tax Regionale a Charge

An 'attestation mutuelle' is always given out by your mutuelle.

It's the medical certification you need to prove that you should be exempted from this tax.

This is the "taxe régionale à charge des chefs de famille (Région de Bruxelle-Capitale)", and you don't have to pay it lorsque "un membre du ménage" est atteint d'une infirmité grave et permanente le rendant totalement et définitivement incapable de quitter sa résidence sans l'assistance d'un tiers."

How come I have to pay more than a someone else? I live in watermael and she in place jourdan. Is that why??