Japanese Green Tea

Japanese green tea and soft water are inseparable, and not by accident. Japan's volcanic geology produces naturally soft tap water (typically under 100 mg/L hardness), and the tea culture evolved in that context. Sencha, gyokuro, and matcha are all processed and brewed to express qualities that hard water suppresses: vivid green colour, clean umami, a smooth rather than astringent finish, and the subtle sweetness that the Japanese call amai. Calcium at 10 ppm and magnesium at 3 ppm keep the water close to the natural Japanese baseline. Higher calcium would bind with the tea's catechins and amino acids, muting the umami that is the signature of good gyokuro. Higher magnesium would introduce a bitter, astringent edge that competes with the tea's own delicate bitterness (which in Japanese tea culture is valued, not avoided, but only when it comes from the leaf).

Bicarbonate at 25 ppm provides just enough buffering to keep the pH stable without alkalinising the brew. The colour of the liquor responds directly to this: a well-brewed sencha in soft water is a clear, pale gold-green. The same tea in hard water turns dull and yellowish, and a calcium-carbonate film may form on the surface.

For gyokuro, which is brewed at very low temperatures (50–60°C) to maximise L-theanine extraction and minimise catechin release, soft water is not optional. The low temperature and short steep time mean fewer minerals are needed to facilitate extraction, and any excess shows up immediately as off-flavours. Matcha, where the entire leaf is consumed as a suspension, is similarly unforgiving. Tokyo's municipal water (which TWD already covers as a coffee profile) sits in a similar range, though the rationale for tea is different: coffee cares about extraction yield and flavour balance; tea cares about colour, clarity, and the umami-astringency axis.