Water for Tea — Temperature and Quality

Tea is approximately 99% water by weight. Water quality and temperature are the two variables most beginners neglect and most experienced drinkers obsess over. A fine tea brewed in the wrong water produces a flat, harsh, or lifeless cup; average tea brewed in good water at the right temperature often exceeds expectations.

Lǔ Yǔ (陆羽), the Táng dynasty tea sage, wrote in the Chá Jīng (茶经, 780 CE): "Mountain spring water is best; river water next; well water worst." The same principle holds today — natural filtration through rock and mineral layers produces the ideal brewing water.

What TDS level is best for tea?

TDS (Total Dissolved Solids) measures mineral content in mg/L. The sweet spot for tea is 50–150 mg/L:

• Below 50 mg/L (distilled, RO-filtered without remineralisation): flat, lifeless brew — minerals carry flavour compounds and affect extraction chemistry
• 50–150 mg/L: optimal range; clean, complete extraction
• 150–200 mg/L: acceptable; flavour begins to show some dulling
• Above 200 mg/L: hardness dulls aroma; produces flat or chalky taste
• Above 300 mg/L: calcium and magnesium interfere with polyphenol extraction; tannins become harsh

Practical recommendations (in order of preference):

1. Still mineral water with TDS 80–150 mg/L (check the label)
2. Filtered tap water (activated carbon removes chlorine)
3. Tap water left open 30+ minutes (allows chlorine to dissipate)
4. Avoid: distilled, RO without remineralisation, tap water TDS > 300 mg/L

Chlorine note: Most European tap water contains residual chlorine. Chlorine kills volatile aromatic compounds — it will noticeably degrade a fine green or white tea. Carbon filter or 30-minute open-air rest eliminates it.

Historically, Huì Quán (惠泉) spring water from Wúxī, Jiāngsū — with a TDS of approximately 120 mg/L — was considered the ideal water for tiě guānyīn. The 8th-century classification by Lǔ Yǔ placed it in the top tier of Chinese spring waters.

TL;DR: TDS 80–150 mg/L is the target. Filter out chlorine. Avoid distilled (too low) and hard water (too high). A variable-temperature kettle + filtered tap water at the right TDS = practical optimum for home brewing.

Temperature by tea type

Water temperature controls which compounds are extracted and at what rate. Lower temperatures suppress bitter catechins and preserve volatile aromatics; higher temperatures extract everything more rapidly.

If-then rule: If brewing rock oolong below 95°C → flat, woody result with no mineral character. If brewing green tea above 85°C → harsh, bitter, aromatic compounds destroyed.

Measuring without a thermometer: Boil water fully, then cool. 100°C → 80°C takes roughly 3–4 minutes in an open vessel; 100°C → 70°C takes 6–8 minutes. A variable-temperature kettle is the highest-ROI tea equipment purchase.

The boiling question

The boiling stages: Watching a traditional kettle, distinct bubble stages appear before full boil:

• Shrimp eyes (虾眼 xiā yǎn): tiny bubbles forming at bottom, ~70°C
• Crab eyes (蟹眼 xiè yǎn): larger bubbles, ~80°C
• Fish eyes (鱼眼 yú yǎn): clusters rising, ~85°C
• Full rolling boil: 100°C at sea level

These stages align approximately with target brewing temperatures for different tea types — useful if using a traditional kettle without temperature display.

Re-boiling: Repeatedly boiled water concentrates dissolved minerals and loses dissolved oxygen. Traditional Chinese tea culture considers repeatedly-reboiled "dead water" (死水 sǐshuǐ) inferior for fine teas. For daily use the effect is minimal; for delicate green and white teas, use freshly drawn and freshly boiled water.

Altitude

Water boils at approximately 1°C lower per 300 m of altitude elevation. Practical implications:

• 1,500 m → water boils at ~95°C
• 3,000 m → water boils at ~90°C

If brewing pǔ'ěr or roasted oolongs requiring 100°C at altitude → a pressurised kettle is the only solution. At sea level or moderate elevation (< 1,000 m), altitude is irrelevant.

Related

• Gōngfū Brewing Guide
• Gàiwǎn
• How to Store Tea

FAQ

Which bottled water brands work well for tea in Europe? Volvic (TDS ~109 mg/L) is widely available and works well for most teas. Evian (TDS ~357 mg/L) is too high — it dulls lighter green and white teas noticeably. Buxton (~280 mg/L) is borderline. San Pellegrino (~1,000 mg/L) is too hard for any fine tea. For delicate teas, low-mineral waters like Spa Reine (~27 mg/L) or Volvic work best; for roasted oolongs and pǔ'ěr, slightly higher mineral content (100–150 mg/L) adds body without flattening. Check labels for TDS or "dry residue at 180°C."

Does a Brita filter make tap water good enough for tea? Yes for chlorine removal — activated carbon filters eliminate chlorine effectively, which is the primary concern for fine teas. The limitation: Brita's ion-exchange resin softens hard water only moderately and has a short-lived effect. In soft-water areas (TDS < 200 mg/L), Brita-filtered water works well. In very hard water areas (TDS > 300 mg/L), Brita alone is insufficient — supplement by blending with low-TDS bottled water or use a reverse osmosis filter with remineralisation.

Does the kettle material affect the water? Measurably, yes — though the effect varies. Iron and clay kettles (cast iron tetsubin, clay yùshū wēi) soften the water's mouthfeel slightly and reduce perceived astringency; this is documented in traditional Chinese and Japanese tea literature and supported by modern observation. Stainless steel is neutral — no effect. Plastic kettles can leach subtle flavour compounds, particularly when new; this diminishes with use. For fine teas, stainless steel or glass is the practical choice if you don't use a traditional kettle.

What should I do if I only have hard tap water? Two practical approaches: (1) blend hard tap water with low-TDS bottled water in roughly 1:1 ratio — this cuts hardness by half without going to zero minerals; (2) use a carbon filter to remove chlorine, then accept some flavour dulling — hard water brews are still enjoyable, just less refined. Avoid: adding lemon juice to "soften" (this only acidifies, it doesn't reduce mineral content). For regular fine-tea brewing in a hard water area, a small reverse osmosis unit with a remineralisation cartridge is the long-term investment.

Does water temperature matter for cold brewing? Cold brewing is specifically defined by using cold or room-temperature water — no heating at all. Temperature matters in a different way: colder water (fridge, ~4°C) produces a slower, sweeter extraction over 6–8 hours, preferentially pulling amino acids over catechins. Room temperature (~20°C) extracts faster and produces slightly more body. Both work; fridge extraction gives the cleanest, sweetest result for green and white teas.