3 ideas
Tea quality is lost at any one of nine sequential points: manufacture, discernment, utensils, fire, water, roasting, grinding, boiling, and drinking. Each has a characteristic error: leaves picked on a cloudy day and dried at night are badly made, and judging tea by chewing it or sniffing its aroma is not true discernment. A cup is only as good as the weakest stage in the chain.
Water temperature is judged visually in three stages. At the first boil, bubbles like fish eyes rise with a faint sound, and salt is added. At the second, bubbles stream from the edges like strung pearls, so a ladle of water is set aside, the center is swirled, and the powdered tea is added. At the third, the water surges like breaking waves, and the reserved water is poured back to stop the boil and protect the froth; water boiled past this point is 'old' and unfit to drink.
Mountain water is best, river water second, and well water worst. Within mountain water, take the slow seep from stone pools. Avoid torrential or cascading water, which causes throat ailments, and drain stagnant valley water before use because it may carry toxins. River water should be drawn far from human settlement, and well water only from wells in heavy use, because freshness and gentle movement determine purity.