The ancient Chinese knew that pure water was essential for making good tea (green tea). The Taoists use porcelain trays to collect rain water or melting snows to get high-grade pure water to make tea. The best water to make tea was collected from the snow that fell on the winter plum blossom, or from the morning dew on the lotus leaves. Of course, these were waters without pollutions or contamination with metals. Now we know that metals, especially iron, in the hot tea are catalysts that may promote oxidation of tea catechins, especially EGCG. Chlorines and detergents also cause degradation oxidation of green tea.
Deionized Water – our green tea is best brewed in deionized water, such as distilled water or water purified by reverse osmosis. All recent science-based research works, which prove the health benefits of green tea in the laboratories, have been based on using green tea prepared in deionized water. Green tea brewed in tap water containing chlorine and iron tends to have a more bitter taste.
Filtered Water — Filtered water has no scientific definition. Its quality depends on the kind of filters used.
Bottled Water — If the bottled water is purified by distillation or by reverse osmosis, it is good to use. However, the solutes in a bottle of spring water are naturally variable from spring to spring.