Which device has the greatest potential to cause contamination if a cross connection occurs?

• A. A chemical dosing pump
• B. A water softener brine tank
• C. A stormwater drainage inlet
• D. A pesticide mixing tank

Answer: (D)

Cross-connections create a path for contaminants to enter the drinking-water system, so the danger level depends on how toxic and concentrated the non-potable substance is. A pesticide mixing tank contains concentrated toxic chemicals; if backflow occurs, those pesticides can rapidly contaminate the distribution system and pose serious health risks to consumers. Other options involve substances that are either typically controlled with backflow prevention (chemical dosing systems) or, like a brine tank, can contaminate water mainly by taste or sodium content rather than causing immediate toxic hazards. Stormwater inlets pose an external contamination risk, but the immediate health danger from concentrated pesticides entering the supply is greater.