What causes Backflow?

Backflow is caused by mainline piping failures or drafting due to high demands. For example, it is a condition that can occur when the drinking water system pressure drops below that of the fire protection system, drawing the fire protection system water back into the drinking water system. Another instance is while using a pesticide attachment on the garden hose, the pesticide may be siphoned back up the hose and into your pipes if the water pressure suddenly drops. As a result, bacteria, chemicals and poisons can contaminate your drinking water.