Tea consists for 99 percent of water and water contains a lot of dissolved solids: organic and inorganic. Organic solids stem from everything that lives like animals and plants; inorganic solids can be found in particles that don’t live like sand and stone. The more dissolved solids in water, the dirtier and less drinkable the water and hence the tea is.
We call the total amount of dissolved solids TDS: Total Dissolved Solids. A special TDS-meter measures the dissolved parts per million (ppm). Tea that is made with water with a high TDS tastes less, contains a foam and has a darker color. In the western world tea water from the tap is drinkable, but can contain a TDS of several hundreds.
Many avid tea drinkers use bottled water of filtered water to make tea. The lower the TDS the better the tea tastes.