<P> A backflow prevention device is used to protect potable water supplies from contamination or pollution due to backflow . </P> <P> In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower, or other fixture . Water pressure may fail or be reduced when a water main bursts, pipes freeze, or there is unexpectedly high demand on the water system (for example, when several fire hydrants are opened). Reduced pressure in the pipe may allow contaminated water from the soil, from storage, or from other sources to be drawn up into the system . </P> <P> Backflow means the undesirable reversal of flow of a liquid, gas, or suspended solid into the potable water supply; a backflow preventer is designed to keep this from happening . Points at which a potable water system connects with a non-potable water system are called cross connections . Such connections occur naturally in appliances such as clothes washers and dishwashers, but they must be carefully designed and installed to prevent backflow . Another common location for a backflow preventer is the connection of a fire sprinkler system to a water main, to prevent pressurized water from flowing from the fire suppression system into the public water supply . </P> <P> Back - siphonage occurs when higher pressure fluids, gases, or suspended solids move to an area of lower pressure fluids . For example, when a drinking straw is used to consume a beverage, suction reduces the pressure of fluid inside the straw, causing liquid to move from the cup to inside the straw and then into the drinker's mouth . This is an example of an indirect cross-connection, undesirable material being pulled into the system . </P>

Where should a backflow prevention assembly be located