Choosing a source
There 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.
What it is
Tap water is whatever your utility delivers, treated and usually mineralised. Filtered tap has been run through a household filter, most often carbon, to remove some of the treatment chemical and a share of the minerals. Bottled spring water is drawn from a natural spring and carries whatever mineral balance that spring has. Bottled mineral water is regulated to guarantee a minimum mineral content, often a high one. Distilled water has had almost everything removed by evaporation and condensation. Reverse osmosis water is pushed through a membrane that strips out nearly all dissolved solids. Well water is untreated groundwater drawn straight from a private supply.
What it does to your tea
A treatment chemical in tap water can carry straight into the cup as an off taste (see treatment). Filtered tap usually keeps enough minerals for a normal extraction while losing that taste. Bottled spring water, drawn through rock rather than a cartridge, often lands in a comparable mineral range. Bottled mineral water can blunt a delicate tea, and where it is high in bicarbonate rather than merely high in minerals, it darkens the liquor too (see alkalinity). Distilled and reverse osmosis water are stripped of the calcium, magnesium and bicarbonate that extraction actually needs, so a brew from either tends to taste thin rather than clean. Well water's mineral load depends entirely on the ground it passed through and can run very hard.
What to aim for
Aim for a source with a moderate, balanced mineral content rather than none at all or a heavy dose. ISO 3103, the international standard for preparing tea for tasting, explicitly warns that distilled water will not give a representative brew and instructs testers to use water resembling ordinary local drinking water instead. That is a reasonable default outside a lab too: something close to typical tap water, with the treatment chemical removed, beats either extreme. If you are comparing bottled waters, read the label rather than the marketing, since 'spring' and 'mineral' are different products with different mineral content.
What you can do about it
If your tap water tastes clean and its treatment chemical is easy to filter out, a basic carbon filter jug is usually all you need. If distilled or reverse osmosis water is genuinely your only option, do not use it straight: cutting it with a little ordinary tap or mineral water restores enough mineral content for a normal extraction. For bottled water, try more than one brand before settling, since mineral content varies a great deal between springs. Well owners should start with a water report rather than guessing, because hardness on a private supply can sit far outside the range a filter jug is designed for.
What people get wrong
The biggest one is treating 'purest' as 'best'. Distilled and reverse osmosis water are not a safe default: stripped of minerals, they leave extraction with less to work with, and the resulting cup tastes flat rather than clean. Confusing bottled spring water with bottled mineral water is another, since the label distinction is real and the two behave differently in a teapot. And bottled water of any kind carries a real environmental cost worth weighing against how much better it actually makes your tea, particularly when a filter jug gets most of the way there for a fraction of the waste.
Sources
- distilled water will not give a representative brew ISO 3103:2019, Tea: preparation of liquor for use in sensory tests