A filter coffee is about 98.6% water. Berlin tap water is hard — around 18 °dH — and it flattens exactly the delicate, acidic coffees people pay extra for.
You do not need a lab to fix this. A jug filter takes the hardness down far enough for most coffees, and a bottle of low-mineral still water takes it the rest of the way. Try the same coffee, brewed the same way, with both. The difference is larger than the difference between most grinders.
If a coffee tastes dull at home and bright in our shop, it is almost always the water.
We are not suggesting anyone buy a remineralisation kit. Just that before you blame the beans, or the grinder, or yourself, try the bottle.