In which situation can back-siphonage occur?

Back-siphonage occurs when there is a negative pressure in the water supply system, which can pull contaminants into the clean water supply. This phenomenon often takes place during situations where there is a sudden drop in water pressure. One common scenario where this can happen is when a water main breaks. When the pressure drops due to the break, it can create a vacuum effect that draws water, possibly contaminated, from a lower elevation source or a connected system back into the potable water supply.

Understanding back-siphonage is crucial since it can compromise drinking water safety. The other situations presented do not create the negative pressure conditions necessary for back-siphonage to occur. For instance, heating water typically does not lower pressure in a manner that causes siphonage. Heavy rainstorms can affect surface water but usually do not impact the pressure in the water mains significantly. Regular water maintenance, while it may involve temporary adjustments to water pressure, is typically managed to avoid creating back-siphonage.