Back siphonage can occur when which scenario occurs?

• A. Fire Department Pumping Large Amounts of Water From a Fire Hydrant
• B. A Closed Valve In The Line
• C. A Low Water Supply
• D. A Clogged Filter

Answer: (A)

Back siphonage happens when the supply pressure in the drinking water system drops, pulling water back into the system through any cross-connections. When a fire department is pumping large amounts of water from a fire hydrant, the sudden high flow can cause a significant drop in pressure downstream. That negative pressure can draw dirty or non-potable water from irrigation pipes or other connected lines back into the potable supply if a cross-connection exists. The other situations don’t create that pressure dip needed for siphoning: a closed valve tends to create backpressure and push water away, a low overall water supply reduces pressure but doesn’t necessarily create a siphon without a cross-connection, and a clogged filter simply restricts flow rather than generating a negative pressure that pulls water back.