While the variety of tea leaf, where and when it is grown, and how it is brewed have traditionally been considered the main factors in tea flavour, water as the primary “solvent” plays a critical role. Water is more than 99% of the tea brew, and even slight variations in its chemical composition or physical characteristics can dramatically change the taste, aroma, colour and extraction of all the beneficial substances. Even with solid varieties and the perfect brewing method, poor quality or inappropriate water can ruin the flavour of the brewed tea.

Below is a full scientific analysis of how the chemical composition and physical characteristics of water will affect the flavour, aroma and health benefits of tea.

 Mineral composition of water and extraction of flavour compounds in it.

Different types of water (such as distilled, mineral, tap water) will affect differently the solubility of catechins, theaflavins, pigments and other bioactive substances present in the tea leaf, viz:

  • water hardness (calcium and magnesium content) reduces the level of extracted catechins and tannins, reducing antioxidant activity and making the flavour flatter (‘The Influence of Water Composition on Flavour and Nutrient Extraction in Green and Black Tea’, Melanie Franks, Peter Lawrence, Alireza Abbaspourrad, 2019)
  • soft water (or its low hardness) promotes better extraction of catechins and consequently provides a richer colour and flavour to the tea. Studies have shown that green and black tea brewed in distilled water will always have a brighter colour and stronger flavour compared to tea brewed in hard water (‘Studies on the Properties of Water for Tasting of Tea’, Atsushi Kubota, Tadakazu TAKEO, Toshio HARA, Hiroshi Saito, 1959)
  • water with high salinity (e.g, spring or mineral water) will impair the extraction of polyphenols and even caffeine, which negatively affects the flavour and antioxidant activity of tea (‘Effect of water quality on the main components in Fuding white tea infusions’, Haihua Zhang, Yulan Jiang, Yangjun Lv, Junxian Pan, 2017)

 Water temperature and its physical properties are affected in this way:

  • higher temperature accelerates the release of caffeine and catechins into the water, but also clearly enhances bitterness and astringency, especially evident in green tea (“Health Functions of Compounds Extracted in Cold-water Brewed Green Tea from Camellia Sinensis L. ‘, Manami Monobe, 2018)
  • when tea is brewed in cold water, amino acids (e.g. theanine) are well extracted, giving a mild, “umami” flavour, with minimal bitterness (’Health Functions of Compounds Extracted in Cold-water Brewed Green Tea from Camellia Sinensis L.”, Manami Monobe, 2018)

 Influence of pH and salts.

pH and the presence of chlorides, sulfates, carbonates in water directly affect the colour, clarity and taste of the finished tea thus:

  • at elevated pH, studies have observed increased bitterness and darkening of the brew, especially in green teas, due to oxidation of catechins (‘The Influence of the Property of Water on the Tea Infusion’, Yoshio KUWABARA, Tadakazu TAKEO, 1955);
  • sodium salts at concentrations >200 mg/L cause a brackish taste and inhibit the opening of tannins and aromatic molecules;
  • chlorine, which is often present in tap water, can impart an unpleasant odour and taste, negatively affecting organoleptics (‘The Influence of the Property of Water on the Tea Infusion’, Yoshio KUWABARA, Tadakazu TAKEO, 1955);

 Effect of electrolytes and structured water.

The use of such water as cathodic water obtained by weak electrolysis will result in a brighter green colour, milder flavour and increased dissolution of catechins (EGCG, ECG) without excessive bitterness (‘Effects of Weakly Electrolyzed Water on Properties of Green Tea Infusion’, 2007, Eiko Arai, Sayuri Kawamura).

 Antioxidant activity of tea and different water.

Catechins (especially EGCG), are key components of green tea that provide its high antioxidant activity. Their content depends significantly on the interaction with minerals in water as follows:

  • water with high pH and mineral content clearly reduces the yield of EGCGs in the brew, while obviously decreasing the antioxidant potential of tea (‘Effect of Brewing Water on the Antioxidant Capacity of Green Tea Infusion with DPPH Assay’, 2022, Qing-Qing Cao, Yan-Qing Fu, Cheng-Bin Zhang).
  • although Ca²⁺ and Mg²⁺ ions at certain concentrations enhance EGCG activity through a synergistic effect.

  Organoleptic parameters and consumer preferences.

Sensory studies of brewed tea have shown that:

  • distilled and bottled water imparts more intense colour, strength and bitterness to the finished beverage, this is particularly strong in green teas (‘The Influence of Water Composition on Flavour and Nutrient Extraction in Green and Black Tea’, Melanie Franks, Peter Lawrence, Alireza Abbaspourrad, 2019)
  • drinking water with low salinity is perceived by tasters as the most pleasant in taste – it gives an optimal balance between bitterness, sweetness and softness (‘The types of brewing water affect tea infusion flavour by changing the tea mineral dissolution’, Fuqing Bai, Guijie Chen, Huiliang Niu, 2023)
  • hard water, on the other hand, clearly impairs the flavour and leads to cloudiness of the prepared infusion, reducing visual perception (‘The effect of membrane-processed water on sensory properties of Oolong tea drinks’, N. J.N Yau, Y.J Huang, 2000)

Duration of brewing and dynamics of extraction into water

Studies show that optimal extraction of flavour substances is achieved at a temperature of about 80 °C with infusion for 3-5 minutes. However, it should be noted that changes in brewing speed affect the extraction of different groups of compounds: catechins, caffeine, amino acids are extracted at different stages (‘Optimum conditions for the water extraction of L-theanine from green tea’, Quan V Vuong, Costas E Stathopoulos, John B Golding, 2011).

Recommendations for ideal brewing

Based on the above and other scientific evidence, we draw the following general conclusions:

1. Only soft water with low salinity (this is about 50-100 mg/l of dissolved substances in it) should be used.

2. Also chlorinated or very hard water (Ca²⁺ and Mg²⁺ > 150 mg/l) should be avoided if possible.

3. A neutral pH (approx. 7.0) is the optimum pH.

4. Bottled water for brewing green tea, oddly enough, provides the maximum yield of catechins in the brew.

5. For black tea, a slightly higher mineralisation is acceptable, but it would be good to avoid a brackish aftertaste.

Recommendations from nutritionists and technologists.

Experts in these fields tend to come to similar conclusions, they advise:

  • to use filtered or bottled water with low mineralisation;
  • always avoid boiling hard water, especially when brewing green tea;
  • experiment with the temperature and infusion time for each particular type of tea – this has a strong influence on the flavour characteristics and benefits of the tea;

In conclusion, we can say the following: water quality is one of the most important, but often underestimated, factors in the quality of tea. It is the chemical composition of the water that can both enhance and inhibit the key flavour components in the brew. Therefore, choosing the right water is a subtlety that not least influences the best possible tea.