The video in the clip explains the fundamentals of back flow prevention.
Backflow prevention is not sufficient to keep the entry of water from various sources in your water source. The potable water would be damaged by water from chemicals, cooling systems or stagnant fire suppression systems, and main line breaks to the sewer.
Back flow prevention companies will work with the government and utilities companies to stage back flow protection systems at important places. There could be hundreds of them in your city, alone. A lot of them are located operating in lower risk areas, but it’s safer to be cautious over to be sorry.
Two main forms of backflows that must be avoided include back pressure and backsyphoning. Back pressure happens an indication that the supply of water to the facility is over stressed and requires relief returning to the water supply.
When the correct measures are not taken to clean the water source that is contaminated and back syphoning happens when pressure from elsewhere can cause water to be taken into the drinking water source. Below is a video that provides more information.