How to Avoid Contamination
When water flows backward through the water supply system, it is called backsiphonage or backflow. When that water is accidentally mixed with hazardous chemicals or bacteria, it is called dangerous.
The danger comes when a hose is connected to a harmful substance. If the pressure in a water main drops while your hose is submerged in contaminated water, then the water and hazardous pollutants could be sucked back into your pipes and drinking water supply. Water pressure drops are not uncommon; and can happen when firefighters battle a nearby blaze, or before utility crews repair a broken main.