Drink tap water
Whether on the road or at home, the easiest way to reduce packaging and save money is to switch from mineral water to tap water. Germany has the highest quality tap water in all of Europe, because it is constantly monitored.
In tests it also regularly performs better than mineral water from wells or springs. Some of these are contaminated with germs or contain high amounts of nitrate or only very few minerals.
The water can be easily bottled for your daily use. Stainless steel or copper bottles are suitable for take-away instead of plastic. It is important to make sure that they are not coated with plastic or silicone on the inside. Copper has the advantage that it kills bacteria. At home you can simply fill the water into old wine bottles or other nice bottles that you like. You don't always have to have a carafe.
If you need some fizz, it's worth buying a home carbonation system. Again, choose the version with glass bottles rather than the one with plastic bottles. By the way, plastic also has the disadvantage that it is easily scratched and micro-organisms, dirt and mould tend to collect in the scratches, which is difficult to remove. Glass is therefore a clear favourite.