Many people wonder what backflows are for, and why you need them. There are many things backflows do but the main reason why we have them is to protect the health and safety of the public. They prevent the reversal of flow of a liquid, gas or solid from getting back into the potable water supply. Most backflows for a residential application are used for irrigation. Once the potable water (drinkable water) goes through your irrigation system it is considered non-potable (Non-drinkable/contaminated) and therefore must have a suitable backflow prevention device according to the authority having jurisdiction.