Drilling fluid is used in virtually all types of wells, even when a water well is going into place. The fluid is used to prevent other types of fluid from building back through the bore hole. Without an ability to control this buildup of fluid, it would be virtually impossible to drill a well effectively. With that being said, there are additional uses for drilling fluid aside from just keeping the flow of water, oil or gas in check. Drilling fluid is frequently used to keep the massive drilling bits used for these holes cool. If the drill bits were to overheat, they would fail and in some cases, they could start a fire or even cause an explosion. The fluid is used to prevent any of these things from occurring and to extend the life of the drilling bits themselves. In some cases, the fluid that is used is also an integral part of keeping things clean. This is especially important when bearings and other mechanisms have to be kept clean and the fluid in question involves oil.