What is the most basic drink?

It's impossible to definitively say what the "most basic" drink is, as "basic" can be subjective and depend on what criteria you're using.

However, here are some contenders for the title, depending on how you define "basic":

* Water: It's the simplest, most essential, and most readily available drink, and forms the basis of most other beverages. It's just H2O!

* Plain Tea: A simple infusion of water and tea leaves, often enjoyed without sugar or additives.

* Black Coffee: Like plain tea, it's just water and roasted coffee beans.

* Milk: A naturally occurring liquid with minimal processing.

Ultimately, the "most basic" drink is a matter of opinion and depends on your individual definition of "basic".