Soft water as a baseline
Japanese tea producers and specialist roasters generally point to soft water with a total dissolved solids reading of roughly 30 to 80 parts per million for matcha. Soft water lifts amino acid character and reads sweeter on the palate. Hard, mineral heavy water dulls aroma and pushes the cup toward a sharper, more crisp finish that obscures umami.
What Ippodo recommends
Ippodo's published guidance is plain. Use water you enjoy drinking on its own, avoid distilled water because tea needs some mineral content to extract well, and a clean filtered tap is often perfectly fine. Their New York shop runs on filtered tap. The point is balance rather than purity at any cost.
Filters and bottled options
A standard activated carbon pitcher filter usually drops chlorine and softens the cup enough to taste the difference. If your tap is very hard, a bottled spring water in the soft to medium soft range works well. Avoid mineral heavy bottled waters and avoid pure distilled water, since neither extracts matcha cleanly.
Quick taste test
Brew the same 2 grams of usucha twice on the same day with two different waters at the same temperature. Differences in aroma and umami show up immediately even with a modest cup. This is the fastest way to learn what your local water does to your matcha.