In layman's terms, backflow is when water reverses its flow and starts to move into areas where it doesn’t belong — back into the clean water system.
To get more specific, backflow happens when low pressure causes water from a potable water system to makes its way back to where it originated. For example, water that has made its way to your irrigation or pool gets pulled back into your water lines. Modern municipal water systems are generally designed to keep the plumbing that provides clean drinking water to your property separated from the plumbing that transports non-potable water with-in your town or cities. When the checks and balances of this system fail, the result is dirty water making its way back through your pipes and into your home or business.
Because of its high risk, backflow is considered to be a public health hazard. Used water can contain all kinds of chemicals, pathogens, and bacteria that are dangerous to human health, therefore it is imperative thatwe do our part to help avoid a back flow situation.