Water Chemistry: Hardness, pH, and Dissolved Solids

More than 99% of tea liquor is water, and what's dissolved in that water directly affects the liquor's color, aroma, and mouthfeel. When it comes to water for pu'er, three measures come up most: hardness, pH, and TDS. Once you understand what each measures and roughly where Taiwan's tap water falls, choosing water becomes much clearer. For the practical side of choosing and boiling water, read this alongside Water for Tea.

Hardness: Calcium and Magnesium in Water

"Total hardness" measures the combined amount of calcium and magnesium ions in water, usually expressed as the equivalent concentration of calcium carbonate in milligrams per liter (mg/L). Common categories are:

Taiwan's Drinking Water Quality Standards set the upper limit for total hardness at 300 mg/L, as an item affecting palatability and sensory quality.

Why Hard Water Isn't Good for Tea

Brewing tea with hard water commonly causes three things:

1. Duller liquor: calcium and magnesium ions bind with tea polyphenols and pigments, so the liquor tends to darken and lose its clarity.
2. Muted aroma and taste: some polyphenols precipitate after binding with calcium and magnesium, reducing freshness, so the liquor tastes "flat."
3. Tea film and scale: a film that breaks apart easily forms on cooled tea, and teaware and kettles build up white scale. See Cream Down and Foam on Tea.

That said, water so soft it has almost no minerals (such as purified water) can sometimes make tea taste thin. Many people find the range from soft to moderately hard water works best.

Tap Water Hardness Across Taiwan

According to water quality data published by Taiwan Water Corporation (updated July 2026), the approximate range of total hardness in tap water by city and county is:

Taipei City and parts of New Taipei City are supplied by the Taipei Water Department and aren't in the table above; 2018–2019 data cited in a PTS report put Taipei's raw water at an average of about 74 mg/L. Overall, the north is softer and the central and southern regions harder, with Kaohsiung, Yunlin, and Changhua mostly in the hard to very hard range. Differences between districts within the same city or county can also be large; to find out your own figures, check the water quality data Taiwan Water Corporation publishes by township.

Taiwan Water Corporation has also explained that hardness comes from naturally occurring calcium and magnesium, and that water quality in every district meets drinking water standards; hardness affects taste and how tea brews, not whether the water is good or bad.

pH: Acidity and Alkalinity That Affect Liquor Color

pH measures acidity and alkalinity: 7 is neutral, lower is more acidic, higher is more alkaline. Taiwan's Drinking Water Quality Standards require tap water to have a pH between 6.0 and 8.5.

For tea liquor, pH mainly affects two things:

• Liquor color: catechins and other polyphenols oxidize faster in alkaline conditions, so the liquor darkens toward reddish brown; in acidic conditions the color is lighter. That's why squeezing lemon into black tea visibly lightens the color.
• Taste: alkaline water tends to make the liquor taste dull and less fresh; near-neutral to slightly acidic water usually gives a clearer, brighter liquor.

The pH of ordinary tap water shifts somewhat when boiled but mostly stays near neutral, so there's no need to worry too much for everyday brewing; just avoid water that's noticeably alkaline.

TDS: How Much Is Dissolved in the Water

TDS stands for "total dissolved solids," the total of minerals, salts, and small amounts of organic matter dissolved in water, in mg/L. The TDS pens on the market actually measure conductivity and convert it. Taiwan's Drinking Water Quality Standards set the upper limit for total dissolved solids at 500 mg/L.

TDS is related to hardness but not the same: hardness counts only calcium and magnesium, while TDS includes sodium, potassium, chloride, sulfate, and more. So low TDS usually means low hardness too; but water with moderate TDS may or may not be hard.

For brewing pu'er, many tea drinkers prefer water with a TDS of roughly 50–150 mg/L: enough minerals to support the mouthfeel without interfering with the aroma. This is a range based on experience, not a standard.

Practical Tips

1. Know your water first: check the water company's quality data, or measure it with a TDS pen.
2. In hard-water areas: use a water filter or choose bottled water with lower hardness; the difference is especially noticeable with aged tea and tender teas.
3. Boil thoroughly: boiling tap water removes the smell of residual chlorine; during boiling, some calcium bicarbonate precipitates out as scale, which also reduces temporary hardness somewhat.
4. Don't reboil repeatedly: boiling the same water many times lowers its dissolved oxygen, and the tea will taste flat.

For choosing a kettle, see Kettles; for controlling water temperature, see Water Temperature.

FAQ

Why isn't hard water good for tea? Calcium and magnesium in the water bind with tea polyphenols and pigments, dulling the liquor color and muting aroma and taste, and they readily produce tea film and scale.

What does pH affect? Mainly liquor color and freshness. In alkaline water, polyphenols oxidize faster and the liquor darkens; in acidic water the color is lighter. Taiwan's tap water pH standard is 6.0–8.5.

What is TDS? Total dissolved solids, the total amount of substances dissolved in water. Taiwan's drinking water standard caps it at 500 mg/L, and tea drinkers often brew with water of 50–150 mg/L.

Is Taiwan's tap water hard? The north is mostly soft to moderately hard, for example about 42 mg/L in Keelung; the central and southern regions are harder, for example about 131 mg/L in Tainan and about 198 mg/L in Kaohsiung.