Water for tea 水

Editors · October 23, 2026, updated October 25, 2026 · 9 min read

Tea liquor is more than 99% water, so the salts and temperature of that water noticeably change the flavor. For tea, use soft water low in minerals, heated only as hot as the leaf needs.

In China they say "water is the mother of tea." Good leaf brewed in hard water loses to average leaf brewed in soft water: the liquor darkens, the aroma goes dull, and a film forms on the surface. So when the tea doesn't taste right, check the water first, then the leaf, and only then your own hand.

What in the water affects tea

Not every number on a water report matters for tea. The ones that do are hardness, alkalinity, total dissolved solids, iron and chlorine.

Hardness is calcium and magnesium. The harder the water, the fewer catechins reach the liquor, and the darker and heavier the tea. Green tea is the most sensitive: Chinese tasting panels found that Longjing tasted best in purified water and in slightly acidic spring water low in calcium and magnesium. Black tea suffers from too much magnesium. In one experiment, sweetness and umami dropped at 16 mg/l, and the best cup came at 4 mg/l. Dark tea is the least sensitive to water composition.

Alkalinity (bicarbonate) pushes the liquor slightly alkaline, which speeds up polyphenol oxidation. Green tea darkens, and black tea turns bitter. Above pH 7 the aroma suffers.

Iron and manganese bring a metallic taste and turn the liquor blackish brown. Chlorine becomes a problem from 0.5 mg/l because of its smell. At about 200 mg/l, table salt already tastes salty.

How many minerals you want

There is no single number, and the guidelines disagree:

• the Tea Research Institute of the Chinese Academy of Agricultural Sciences: total dissolved solids below 50 mg/l;
• the Chinese standard for "tea water" T/CTSS 32-2021: conductivity of 10–100 µS/cm, calcium no more than 12 mg/l, magnesium no more than 8;
• the US Tea Association, as relayed by Barista Hustle: 50–150 ppm and hardness around 80 ppm.

The first two agree, and the third is two to three times looser. In practice, the more delicate the tea, the closer you stay to the low end. Just don't go to zero, because fully demineralized water makes an insipid cup.

Tap, bottle, filter

Judge tap water by its smell and by your kettle. White scale on the walls means hard water. Russian drinking water rules allow up to 7 mg-eq/l, about 350 mg/l CaCO₃. That is a sanitary ceiling, not a target for tea: water like that is four times harder than water at 84 mg/l.

What each treatment does, and what it leaves alone:

Japanese producers advise boiling tap water for several minutes to drive off the chlorine smell, then letting it cool to the temperature you need. That won't deal with chloramine, which takes activated charcoal and a long contact time. Magnetic "softeners" do not soften water.

On a bottle, read the dry residue. In the EU, "very low mineral content" means no more than 50 mg/l, and "low" up to 500. If the label says "contains calcium" (over 150 mg/l), "contains magnesium" (over 50) or "contains bicarbonate" (over 600), skip it for tea. A "for tea" claim without composition figures guarantees nothing.

Change filter cartridges on schedule. A BRITA MAXTRA+ cartridge, for example, is rated for 100 l at a carbonate hardness of 10–12 °dH and for no more than four weeks, and its capacity drops in harder water. Scale in the kettle spoils water too. It is temporary hardness that has settled out, so descale the kettle now and then.

Temperature by type

The more delicate the leaf and the lighter the oxidation, the cooler the water. Boiling water scalds the young buds of green tea, while the dense leaf of a rock oolong or of pressed pu-erh needs all the heat it can get to open up. The reason is chemical: amino acids (theanine) dissolve even in warm water, while the bitter galloylated catechins dissolve in noticeable amounts only above 70–80 °C.

Japanese teas go lower still: gyokuro is brewed at 40–60 °C, top-grade sencha at 70 °C and ordinary sencha at 90 °C, while bancha and hojicha take boiling water. To cool the water, pour it into a yuzamashi (a cooling bowl) or into the cups. Each transfer takes off 5–10 °C.

The table gives the temperature of the water in the kettle; in the teapot it is lower. In Hojo Akira's test, boiling water poured into cold clay pots was down to 79 °C after a minute in a 100 ml pot, 83 °C in a 140 ml pot and 85 °C in a 300 ml pot. After two preheats, the small and large pots held 89 and 91 °C. That is why you warm the teaware first and only then work out how much leaf to use and how long to steep it.

At altitude the boiling point drops by about 1 °C for every 300 m. At 1,500–1,800 m it boils at 95 °C, at 4,800 m at 84 °C. In the mountains, that matters for oolongs and pu-erh, which need a full boil. At sea level, weather shifts the boiling point by only ±1 °C, too little to affect flavor.

Should you reboil water?

The common belief is that reboiled water "loses oxygen" and makes tea flat. America's Test Kitchen put this to the test, comparing tea made with freshly boiled and reboiled water (three repeats each), and found no difference in flavor. The first boil already drives off so much dissolved gas that a second one changes little. Joe Schwarcz of McGill University also ran the numbers on "concentrated harmful substances": after boiling off half the water, the fluoride content differs by about 10%, which is negligible.

That does not make endless boiling a good idea. Repeated boiling and cooling leaves a suspension of carbonates, concentrates permanent hardness and builds up traces of iron and copper, and the taste can change. Fill the kettle with fresh water and take it off as soon as it boils or reaches the temperature you need. Pour out whatever is left after the session. In gongfu cha, the water for a dozen infusions is reheated briefly, without letting it boil on.

Lu Yu's three boils

Lu Yu described how to boil water for tea in The Classic of Tea, written around 760. In his day the tea itself was boiled: ground leaf went into boiling water in a cauldron. Lu Yu distinguished three stages. At the first, the bubbles look like fish eyes and the water makes a faint sound; this was when you added salt. At the second, the water at the edges wells up like a spring and bubbles rise like strings of pearls; then you scooped out a ladle of water and put in the tea. At the third, the water heaves in waves. Past that point, Lu Yu says, the water "grows old" and is no longer fit for tea. In the same chapter he ranks mountain water above river water, and river water above well water¹.

Writers of other eras differ on details: for Cai Xiang, "crab eyes" already mean overboiled water, while Lu Yu's "fish eyes" only open the scale. But the habit of watching the bubbles lived on, even if a thermometer in the kettle now often stands in for them.