how do you know if I have water in my boat gas 6 gal. tank, boat is putting along

If your boat is putting along then it sounds like water in the fuel is not a problem.

Get rid of it anyway, fill up with fresh premium.

Clean all you filters, on the tank, inline if applicable, and the screen on the engine.

If that does not solve the problem we will move to the next step.

Tilt tank on end look inside>Did you put oil in the Gas???

empty the tank duh

cant easily. since gas is lighter than water, any water will settle at the bottom of the tank, out of sight.
if its only 6 gallons, just replace the fuel and be done with it

There is a product called Kolor Kut that you add to the gas - it changes color in the presence of water. Better to drain the tank and lines then put in new fuel.