Even outside of the rust that water in the fuel tank will cause, there are more immediate effects. If water makes its way out of the tank and into the rest of the fuel system, your car will run poorly or will break down altogether. In extreme cases, water coming through the fuel injectors will accumulate inside your engine's cylinders causing a condition known as hyrdraulic lockup, or hydro-lock. This can destroy your engine. Water that accumulates in a carburetor can freeze and crack one of the many very delicate parts or passageways in the carb.
For these reasons, water needs to be kept out of the fuel system. Modern fuel tanks have a number of ways of doing this. The fact that a modern fuel system is very well sealed is a huge advantage or those of even the late '80s and early '90s. Unfortunately moisture can begin to build up in your fuel tank by the accumulation of condensation. Many people will use a fuel additive to remove moisture from their gasoline, especially in older vehicles that are more prone to haveing water in the tank. But are these additives doing any good? Are they necessary? Or worse, could they be harming the components of your fuel system?
One of the most popular products on the market is called Dry Gas. If you examine the active ingredient in this and similar products you will see that alcohol plays the most important role. In fact, it's the only ingredient that does anything at all for the most part. Alcohol bonds with water and keeps it from having an effect on the fuel system. The stuff works, it does the job. Additives like this will keep moisture under control, but modern fuel systems may not be as happy adding this much alcohol its components. Why is this? One reason is the delicate -- and cheap -- materials used in modern fuel systems. Low grade rubber and plastics may suffer and degrade when in regular contact with alcohols. But the biggest problem is the fact that the fuel that most people use today is already full of alcohol, as much as 10 per cent. It's called Ethanol, it's made from corn, and I'm sure you've already heard of it. If the fuel you use every day contains Ethanol, there's no need for a fuel drying additive. It's redundant and can increase the level of alcohol in your fuel to levels that can cause degradation.