Understanding what can happen to diesel, why it happens and what to do about is more important than using most popular additive. While it's true taking measures to prevent water being introduced into diesel is prudent, the separator will catch it before reaching injection pump. Routinely checking separator for water and draining any that's present will usually prevent problems.
The main concern with water in seldom used equipment and stored diesel has to do with algae. Algae needs water to grow so no water, no algae. Monitor your source of fuel to see it doesn't contain algae. Watch fuel as it is being poured from storage container to tractor tank for signs of discoloration. If you notice discoloration, treat tractor tank and storage container with algae killer.
Buy fuel only from high volume stations,avoid hole in the wall and deep discount mom and pop places like the plague. That's where risk of getting algae is greatest. A more serious issue with these places is some mix waste oil and solvents with their diesel to boost profit. Operations are occasionally shut down where fluids collected from garages, transmission shops and such are sold for 50 cents per gallon to unscrupulous fuel vendors instead of paying $2 per gallon for EPA approved disposal.
One last word on water additives. DO NOT use same additives as used for gasoline. Those additives bind with water allowing it to pass through separator then damage injection pump and very possibly engine. Strange as it might sound, a bit of water decarbonizes a gas engine which improves performance.
