My last load of fuel from a big supplier was loaded with water.
I use power service as well as biocides for tank treatments.
My suggestion is to have a water drain tap at the lowest point of the tank if you do bulk storage, and use a filtered breather as oposed to an 'open' tank breather.
For in the can / in tank water.. if it is a large amount, I'd crack a fuel line and purge it.
Many tractors have both sediment bowls with water dains, and some even have fuel filters with water drains... make use of them.. often!
Soundguy