Absolutely, and actually you will find this to be the norm and not the exception. In a simplistic statement, pH of water measures the amount of Hydrogen available. Many different chemicals, physical conditions, and substances affect the pH of water.For the pH in a body of water to be even close to the same everywhere, it would have to be stirred and homogenized from shore-to-shore. This is not anything that can be accomplished.
Depending on which source you use, approximately 2% of the water on earth is fresh-water and drinkable. Of that much of it is trapped in ice and glaciers.
Secondly, Pure water does not exist in nature. It can only be produced through the utilization of multi-step filtration systems. If we are referring to “safe” drinking water, that is readily available in plastic bottles, jugs, and of course, if you live in America, from your faucets