Using water instead of coolant in a car's cooling system can be done but should only be considered in an emergency and only for a short amount of time. According to ErictheCarGuy.com, water corrodes the engine quicker than coolant and has a lower boiling point (making it much less effective).
The cooling system is a necessity in cars. Although the gas engines in 2014 cars are much more advanced than older engines, they are still relatively inefficient at converting energy. About 70 percent of a car's energy is lost as heat, and it is the coolant's job to dissipate that heat and keep the engine in working order.