Which of the following scenarios would require using alternate water sources as a preventive measure?

Using alternate water sources is crucial in scenarios where water quality is compromised, which is the case during contamination events. When there is a risk of harmful substances, pathogens, or pollutants entering the water supply, relying solely on the primary water source can pose significant health risks to the population.

Implementing alternate water sources allows for immediate access to safe drinking water and ensures that the community's needs are met while addressing the contamination issue. This proactive approach helps to mitigate public health risks and provides a crucial safety net until the primary water source can be tested, treated, or deemed safe again.

In contrast, heavy rainfall might replenish water sources but does not necessarily indicate a need for alternate measures if existing sources remain unaffected. Regular maintenance checks and routine system updates are important for ensuring the overall functionality and reliability of the water distribution system but do not directly relate to responding to contamination threats.