Water
Brewed tea is roughly 98 to 99 per cent water by mass, so what is dissolved in yours matters almost as much as the leaf does. Minerals, dissolved gases and whatever a utility adds to keep the supply safe all shape extraction, colour and how the cup tastes. This section works through the variables that genuinely move a cup and sets aside the ones tea writing argues about without much evidence behind them.
- AlkalinityAlkalinity is your water's capacity to neutralise acid, driven mostly by dissolved bicarbonate. It sounds like a niche measurement, but of everything on a water report it correlates most directly with what happens in your cup: brewed tea is itself acidic, so what actually decides the final colour and catechin content is how hard the water pushes back against that acidity, not the pH the water started with. Two waters can share an identical pH and behave completely differently once tea leaf hits them.
- HardnessHardness is the calcium and magnesium dissolved in your water, reported as a single number in milligrams per litre of calcium carbonate even though most of what is actually there is not carbonate at all. It is the reason kettles fur up, soap will not lather and a used teapot gets a pale ring round the inside. It also measurably changes what a cup of tea does: harder water pulls less flavour out of the leaf and darkens the liquor while it is at it.
- MineralsTea books quote a scatter of different mineral targets for brewing water, and they do not agree with each other because they are not measuring the same thing. Some are counting total dissolved solids, the sum of everything ionic in the water; others mean calcium and magnesium hardness specifically; and at least one figure in wide circulation traces to no verifiable source at all. A cheap TDS pen gives you a single number for all of it, which tells you less than it looks like it does.
- Reboiling, oxygen and fresh waterThree pieces of tea folklore travel together: never reboil water, use water that is highly oxygenated and always start from a freshly drawn tap rather than water that has been standing. Published tea writing splits on all three, with some authors calling them baseless and others repeating them as settled fact. Neither side is quite right. The oxygen story does not hold up, but the caution behind it is not empty either, it is just aimed at the wrong gas.
- Choosing a sourceThere is no single correct water for tea, only a source that suits your tap, your kettle and how much you want to fuss over it. Tap, filtered tap, bottled spring, bottled mineral, distilled, reverse osmosis and well water each bring a different balance of minerals and treatment chemicals to the cup, and the source that sounds purest is often the wrong choice rather than the safe default. What matters is knowing what each one actually gives you before you reach for it.
- Chlorine and chloramineMost municipal water carries a disinfectant to keep it safe between the treatment plant and your tap, and it is a common reason tap water tastes wrong in a cup of tea. There are two chemicals a utility is likely to use, chlorine and chloramine, and they behave very differently once a kettle is involved. Knowing which one is in your water decides whether a jug filter and a few hours of standing will fix the problem or do almost nothing.
What it is
Water carries three things into the cup beyond H2O itself. Dissolved calcium and magnesium, together called hardness, change how much comes out of the leaf. Dissolved bicarbonate, measured as alkalinity, decides how strongly the water resists being acidified by the tea, and that is the one that governs colour. And whatever a utility has added to keep the supply safe to drink rides along with both. None of it shows up by looking at a glass, and two taps a few streets apart can differ noticeably.
How to find out what yours is
The most reliable answer is the one your water utility already publishes. Suppliers issue an annual water quality report, sometimes called a consumer confidence report, listing hardness, pH and treatment method for the exact system serving your address, and most put it online without being asked. In Germany this is a legal requirement rather than a courtesy: suppliers must disclose which of three statutory hardness bands, weich, mittel or hart, their water falls into. A home test kit or a TDS pen can add detail, but the utility's own figures are the starting point, not a guess from taste.
What people get wrong
The one part of this section that is genuinely about the water rather than the tea is altitude. Air pressure drops as you climb and water's boiling point drops with it, continuously rather than at any particular line, though it starts to matter for brewing somewhere above roughly 1,300 metres. A black tea brewed up there is quietly getting cooler water than a sea-level recipe assumes, with nothing on the kettle to tell you so. It is worth knowing your local boiling point once, rather than assuming every kettle's 'done' means the same temperature everywhere.
