Good water makes good tea. Alkaline water or water dissolved with ferric salts makes tea astringent and forms a rusty surface scum on the tea liquid.
Tea brewed with soft water is most palatable.
On most occasions, hard water dissolving only calcium hydrocarbonate and magnesium hydrocarbonte is regarded temperal hard water, when it is boiled those components become incrusting and precipitated on the bottom and wall of the kettle and the hard water becomes soft. Tea made from soft water produces a bright color liquid with pleasant fragrance and good taste. Hard water with heavily dissolved salts turns the tea liquid to dark color with bitter and astringent taste. Its is also unsuitable for making tea. Boiling water for making tea calls for special attention.