What is the most cleanest drinking water?

I'm curious, what exactly constitutes the most clean drinking water? Is it simply water that's free from impurities and contaminants, or is there a specific standard or certification that defines its purity? In today's world, where access to clean water is a growing concern, it's important to understand what sets apart the cleanest drinking water from the rest. Could you elaborate on what factors contribute to the cleanliness of drinking water, and what makes one source stand out as the most pure?