It depends on what year, make and model but for the most part the vehicles built since the 1990's are a sealed/closed system. Water can get in via contaminated fuel from gas station and also a small amount can accumulate from condensation. Regular use of a quality dry gas additive is always a good idea.
It's as simple as buying yourself a water fuel system and installing it into your car. The System has self contained water and when you run electricity through it from your car battery it separates the hydrogen from the water creating HHO. This combined with the gas from your car will improve your mileage by as much as 60% and emit less green house gases. http://www.squidoo.com/how-to-get-fuel-from-water
As of yet I haven't heard of any completely water run cars however you can get a water fuel system that will produce a gas called HHO from water and that will allow your car to run more efficiently for my car (2005 KIA Spectra) it improved my mileage by 60% http://www.squidoo.com/how-to-get-fuel-from-water
No, water is not a fuel.
The car openings all need to be properly sealed to prevent water entry to the car body and then many cars will float. There are numerous holes and seams in the car body that are plugged and sealed but not sufficiently to prevent water entry.
A fuel injection system on a car replaces the need for carburetors.
The diesel fuel system in a vehicle is similar to the fuel system in a fuel injected gasoline driven car. There is a tank to hold the fuel, fuel lines to deliver it to the fuel pump, and fuel lines from there to the injectors that deliver the fuel into the cylinders at the correct time.
Assuming that there is a fuel filter in the fuel delivery system, it depends on how much water is in the tank, as well as where and how the fuel pickup tube is situated. Water will completely plug up a fuel filter and it takes surprisingly little water to do so (as little as a few mLs), but if the fuel pickup is not taking from the very bottom of the tank, a pretty significant amount of water would need to be in the tank to allow water to enter the fuel system.
As you probably know, the fuel system is a sealed system. You probably fueled up with the engine running.the light should go out after you start the car afew times.
Don't know how cold your cold is but, it could be water in the fuel system (ice).
On most modern sealed batteries you do not have to add water. On batteries that are not sealed you should check the battery monthly. If you have to add water only add distilled water and never tap water.
Because there is no need to add water as they are maintenance free for life.
i don't know about older cars but newer ones the tank is actually sealed and is under a vacuum. Basically, no they won't. On automobiles they usually have the fuel cap as the breather. There's usually a small hole or something in the cap. You need something to replace the gas as it leaves. Older cars either vented the fumes to the air or into an "Evaperative Canister". Basically just a can with some charcoal in it to absorb the gas fumes as it expands and contracts and then it has a small hose going to the intake system to be used by the motor to keep the air clean. "Some" of the newer cars have a sealed system that takes care of all that automatically. You have to be careful when replacing a lost fuel cap as some need the cap to have an air bleed hole to let air into the tank. If you put a sealed system type fuel cap on a non-sealed system it will prevent the fuel from flowing.