If the same tea tastes different in two different cities, check the water first before suspecting a change in the tea itself. The odour, hardness, filtration method, and actual temperature of drinking water all influence the brew; this is why European shops should log local water profiles during tea tastings.
A straightforward side-by-side comparison suffices: use the same tea, the same cup, and the same leaf measure and steeping time, altering only the water. First check whether the hot water itself has a noticeable odour, then assess the aroma, clarity, and mouthfeel of the tea liquor. If tap water exhibits off-odours, trial filtered water meeting drinking standards or an alternative drinking water. Avoid altering the water temperature and leaf measure at the same time, or it will be impossible to identify the source of the difference.
Water temperature also needs recording
How long water has rested after boiling does not equal the actual temperature in the cup; the materials of kettles and cups, along with ambient room temperature, all affect cooling rates. If a green tea tastes bitter or astringent, first shorten the steep or trial a slightly lower water temperature; if a Pu-erh fails to open up, check the water temperature and leaf dosage against the product recommendations first. These are practical directions for trial brewing, not universal parameters for all teas.
If a shop aims to replicate a beverage, recording the water used, equipment settings, and actual serving steps is far more useful than merely stating "use good water". Buyers comparing samples should likewise conduct tastings under identical conditions.
If a shop intends to standardise a fixed recipe, filter cartridge replacement dates and hot water equipment settings should also be recorded; shifts in water quality will cause a brewing card to lose its repeatability.