How to tell if i have water in my gas tank or just bad fuel

Hello, the outcome is one and the same. You'll never know how the "bad fuel" got there unless you have evidence. But, water in your fuel and "bad fuel" create the same concern. I will say that unless you have someone who is out to get you, it'd be highly unlikely that someone would pour water into your gas tank, or even have a contraption that could effectively do that. In fact, most people put "sugar" or other debris in the tank as a vandalism measure. Either way, obviously care must be given to ensure your fuel system is cleaned up as needed.