Glass is recommended for the kettle. You can see the color of the Chaga. And the Chaga tea will be the soft and mellow taste.
RO water or soft water is recommended. RO water is water produced by a reverse osmosis membrane water purifier. It is pure water with impurities removed. You can simmer Chaga thickly with RO water. If you make Chaga tea in hard water including a lot of minerals, it will have a thin, hard and gritty taste.