Yesterday, at a friend's house, I had the chance to drink old puerh made with spring water boiled with burning (longyan wood) charcoal on a Nilu similar to the one I have (picture on the left). Each time I drink tea boiled with charcoal fire, it tastes rounder and sweeter than usual. Using this traditional way changes the whole atmosphere. A little bit like BBQ means 'party', burning charcoals warms more than just the water...
Then, as I noticed that my friend had both a tetsubin and an old Japanese silver kettle (picture below), so I proposed that we compare the water boiled from both kettles.
Boiled in the (unglazed) iron tetsubin, the water felt rounder, sweeter. I felt a tiny bit of iron taste.
The water from the silver kettle felt light and pure. Despite the high temperature, I sensed a kind a freshness. My friend agreed and said that the water from the tetsubin had weight (his hands went down), the water from the silver kettle felt light as air (his hands went up). We concluded that both waters were very good. The silver kettle seems an excellent fit for very light and fragrant teas (green teas, light oxidized Oolongs, young raw puerh...). The tetsubin seems to be a better fit for old puerhs and 'heavier' teas in general (roasted Oolongs), where sweetness and a full body feel is more important.