2- Water quality:
Water quality is crucial to the coffee taste since it makes more than 98% of the coffee cup.
Water is a great solvent (especially hot water) because it has the capacity to dissolve all kinds of molecules. Pure water will extract coffee solids differently than water with impurities (basically particles that make water hard, soft, or distasteful).
Usually if the water tastes good as plain water, it might be good for coffee. Unfortunately, that’s not always a guarantee.
The water TDS (total dissolved solids) affect the level of coffee extraction, and needs to be in an acceptable range. Some of the expensive bottled water in the supermarket is too soft (low tds) and will make coffee taste flat. Tap water might be too hard and impart flavors on the cup. Using normal bottled water or using a water filtering system is recommended to get a good coffee.
That’s why specialty coffee shops care greatly about their water quality.