How do you think coffee is made? You infuse water with coffee beans, normally ground. How strong your coffee is depends on the concentration of actual coffee vs. the “base” (water). It’s the same with tea.

Black coffee can be an espresso, or something with more water. Generally speaking, an espresso is more concentrated (and thus stronger) than an Americano.

A 300ml Americano with 1 shot of espresso has a certain coffe-to-water ratio. A 300ml Americano with 2 shots of espresso will have 2x as much coffee content despite it having the same volume.

In any case, an Espresso is mostly water, even the strongest, tinture-level ones. It’s made by literally passing hot water through the beans so the water gets infused with coffee oils and alkaloids. It’s mostly water. In fact, it’s nearly all water.