Water: The Ingredient That Is Ninety-Nine Percent of the Cup
Very hard water flattens tea. Very soft water makes it thin and sour. A middling mineral content works best.
A cup of tea is over ninety-nine percent water, and the mineral composition of that water participates chemically in the brewing. This is not a marginal effect: the same leaf brewed in soft and hard water produces noticeably different liquors.
What the Minerals Do
Calcium and magnesium — the ions responsible for hardness — bind with tea polyphenols. In moderation this rounds the flavour and reduces harsh edges. In excess it flattens the tea, dulls aroma and produces the film that forms on the surface of tea made with very hard water.
Bicarbonate raises pH, which affects how compounds extract and how the liquor appears. High bicarbonate water produces darker, duller tea with less aromatic lift.
The main effects
- Very hard water. Flat, dull, muted aroma; scum on the surface.
- Very soft or distilled water. Thin, sharp, sometimes sour; lacks body.
- Moderate mineral content. Rounded, aromatic, full.
- Chlorine or chloramine. Chemical taste that masks everything.
- High bicarbonate. Darker liquor, reduced aroma, flatter taste.
The Goldilocks Range
Tea specialists generally suggest total dissolved solids in the region of thirty to a hundred parts per million, with low bicarbonate. This is soft to moderately soft water — considerably softer than typical hard-water tap supplies and noticeably harder than distilled.
| Water | Typical TDS | Effect on tea |
|---|---|---|
| Distilled or RO | 0-10 ppm | Thin, sour, lacking body |
| Very soft tap | 20-60 ppm | Generally very good |
| Moderate tap | 60-150 ppm | Good to acceptable |
| Hard tap | 200-400 ppm | Flat, dull, surface film |
| Filtered hard water | Varies | Improved but depends on the filter |
| Bottled spring water | Varies widely | Check the label; some suit tea very well |
Take the same tea to a soft water area and it becomes a different drink. People who move house frequently think their tea has gone off.Osric Delaine
Chlorine
Municipal water is treated with chlorine or chloramine, both of which are detectable in tea and both of which mask delicate aromatics. Chlorine dissipates if water is left standing overnight; chloramine does not.
An activated carbon filter removes both effectively and is the simplest improvement available to most people. A jug filter costs little and makes a noticeable difference, particularly with green and white teas.
Practical Improvements
- Use a carbon filter to remove chlorine and chloramine.
- In a hard water area, consider a filter that also reduces hardness.
- Never use water that has been boiled twice; repeated boiling concentrates minerals and drives off dissolved oxygen.
- Fill the kettle fresh each time rather than reboiling.
- Descale the kettle regularly; limescale affects both taste and heating.
- If using bottled water, check the mineral analysis on the label.
Dissolved Oxygen
Freshly drawn water carries dissolved oxygen that contributes to the perceived liveliness of tea. Reboiling drives it off, which is the physical basis for the traditional instruction to use freshly drawn water.
The effect is subtle and real. Blind comparisons between fresh and twice-boiled water show a consistent preference for the fresh, particularly in delicate teas.
Which Teas Are Most Sensitive
- Most sensitive. Delicate greens, white teas, high-mountain oolongs.
- Moderately sensitive. Lighter blacks, lightly oxidised oolongs.
- Least sensitive. Robust blacks, roasted oolongs, aged puerh.
- Strongly flavoured teas mask water faults that delicate ones expose immediately.
Test it yourself
Brew the same tea with your tap water, with filtered water, and with a bottled spring water of moderate mineral content. Taste them side by side. Most people are surprised by how large the difference is and never go back to unfiltered tap water for good tea.
The Traditional View
Classical Chinese tea writing ranks water sources in considerable detail, generally preferring mountain spring water over river water and river over well. This corresponds reasonably well to modern understanding: mountain springs tend toward low mineral content and low bicarbonate.
It is a useful reminder that the importance of water has been recognised for a very long time, and that the current interest in it is a rediscovery rather than a novelty.