Tea is over 98% water! So using good water is more important than many people realise. Often when customers get in touch about their favourite tea suddenly tasting quite different it has come down to a change in water source. It really does make a dramatic difference.
The following guide to water is the 'ideal' practice but on many occasions it's just not practicle to acheive such as busy restaurant environments. If many cafes and restaurants made the effort they'd find themselves selling a lot more tea and take this into consideration making tea for friends at home... they'll all be asking your secret method of making such good tea!
Firstly it's important to understand that the water you use should not be over-boiled. The flavour and goodness in tea is extracted largely by the dissolved oxygen in water. The boiling of water is dissolved oxygen escaping, so you're best to use freshly boiled water so that as much of the dissolved oxygen has been retained as possible. Tea prepared using water that has been boiled a few times or from a wall mounted boiler that constantly boils will often taste flat in comparison, much of the freshness and goodness is simply never brought out.
The PH balance of water should be between 6-8 but the closer to a neutral 7 is best. High PH is alkaline (bitter) and in combination with elements of hard water (such as calcium carbonate) can contribute to the formation of limescale and produces a darker but dull liquor. Low PH is Acidic (sour)... if too low in can produce a pale, more yellow liquor lacking in body.
If the tap water in your home or workplace has a distinct 'Chlorinated' aroma or taste then you should filter it using a standard filter jug or tap attached. When boiled that Chlorine flavour becomes very prominant in tea, especially lighter tea like green or white tea.
The minerality of water plays a big part in the final quality of the tea. If you are in an area with particularly Hard Water then you should use a water filter as high levels of mineral content in water cause tea to be cloudy and the tea can taste overly bitter, metalic or even salty. If the water is too soft it will be very thin in taste.
Avoid 'Distilled Water' as this has had all minerals removed and some mineral content helps bring out the best in tea.
Minerality is measured in Total Disolved Solids (TDS) and Water Hardness.
Difference between TDS (Total Disolved Solids) and Water Hardness?
TDS is the 'total' impurities of all minerals (including Calcium & Magnesium), salts, metals, cations or anions dissolved in water measured as mg per liter (same as ppm or 'parts per million'). Total Hardness is only Calcium and Magnesium together measured in mg/l(ppm). Usually Hardness falls between 25% to 40% of TDS.
So what is the ideal level for tea?
To be honest different teas suit different water to bring out the best so there is not one rule for them all aside from avoiding the extremes of too high or too low.
The ideal TDS level of water for tea might be between 50-150 mg/l(ppm). Bottled water always gives this measure but tap water can be easily tested with kits or meters purchased through stores that supply equipment for swimming pools or fish tanks.
Water Hardness is ideally not too soft. Much lower than 10 mg/l(ppm) will not allow the polyphenols and goodness in tea to draw out and will lack body. Anything much higher than 120 mg/l(ppm) will start to produce an overly astringent (bitter) cup that is course in texture and lacks any of the aromatic top-notes present in good tea.
As a general guide the World Health Organization (WHO) lists water hardness as the following:
Soft water: Less than 0-60 mg/L
Moderately soft water: 60-120 mg/L
Hard water: 120-180 mg/L
Extremely hard water: More than 180 mg/L