And how does "filtration by nature" preclude removing impurities yourself too? Bottled water isn't supposed to contain a fish, a leaf, or soil. Any reasonable person understands this bit. Those impurities aren't water. They are external elements and are removed with a simple filter.
What cannot be removed as such are the germs, bacteria, chemicals, and other contaminants. You need to instead add disinfectants and/or use a variety of distillation methods. That's what happens at your municipality or on the ship. Clean, natural sources - such as those used by the likes of Evian, Voss, and Fiji - don't need this filtration treatment.
And labeling 101. None of the water, soda, or other beverage labels you see in the supermarket guarantee the exact content in each container. They are measured and reported in bulk. For a water source such as Evian's, it's measured in a large aquifer over a long period of time. You see the bulk averages. Simple logic will tell you that there is nothing extraordinary about, say, 'Sulfates 15'. So there is no need to fudge the numbers - just report the averages you find.