Glass
Glass is the primary component of glasses, which is one of the three essential building blocks in glasses of water. Glasses of water provide people with water, and essential arm and hand excercise that keep people fit enough to bypass the evolutionary trend towards extreme muscle weakness. As humans no longer face any challenges to their survival, muscle levels naturally decrease with each generation, unburdening the person with the extra energy needed to carry that weight, and making more room for pointless footy trivia. Without the strengthening counter effects of glass holding this would be allowed to run it's course until humans could no longer operate their limbs, and the species as a whole would die out around 2072. The same effect is generally observed with glasses containing other beverages, but often a lot weaker and heavily linked to brain leprosy.
As well as this, glasses of water without glass are unable to function. There is no way to contain the water hygenically and effectively as you transport it from the tap to your mouth, and without glass or water, 'of' quickly loses it's electrons and becomes a deadly toxic agent.
Glass is made by mindlessly slaughtering grains of sand, which is okay apparently.