Normally, water flows forward from the city water supply system into your home. Backflow is the ‘backward flow’ into the public water supply. This can be caused by either back pressure or back siphonage of your plumbing system. If water flowing backward contains hazardous chemicals, toxins, or bacteria, this can cause a very unhealthy and even dangerous situation for many people.
Your garden hose is actually the most common cause of backflow. For example, let’s say you’re watering your garden with a pesticide applicator attached to the hose. It can create a drop in water pressure in the supply system that causes a vacuum. This vacuum will pull the pesticide-laced water into your home & possibly your neighbors. The next time you or your neighbor’s turn on a faucet, the water could be laced with toxic chemicals. Water pressure drops are not uncommon, it also can happen while a crew repairs a broken water main or firefighters put out a nearby fire.