Have you ever been at somebody else's house and asked for a glass of water? When you took a sip, you couldn't help but notice it tasted very different from your water at home. You may have thought, "That's weird, I thought water was just water," However, the taste says otherwise.
There are several differences between well water and city water, including the source, quality, reliability, taste, and even how you pay for it. Even city water varies from city to city, so water is certainly not "just water."