Do I buy distilled water at grocery store or a pharmacy? I need it for a medical humidifier. It seems like most of the pharmacies are closed on weekends.
Drugstores like DM or BIPA (or hypermarkets that probably sell destilled water as well) are closed on Sundays and public holidays (and on late evenings and at night on weekdays), however, pharmacies have a coordinated system for 24/7 availability ("Bereitschaftsdienst"), which means that at least one or more pharmacies per district will be open at any given time even on weekends (with an additional fee being charged during nighttime).
I found a store called DM that seems to sell cosmetics and laundry supplies. They had a 5 liter bottle for €1.50.