Which water supply source was not utilized in earlier times?

The centralized treatment of reservoir is the correct answer because, in earlier times, communities relied on more localized and natural sources for their water supply. First, springs and wells provided access to groundwater, while creeks and rivers offered surface water for drinking, bathing, and irrigation. Additionally, rainwater harvesting has been a traditional practice in many cultures, allowing people to collect and use rain as a vital resource.

Centralized treatment and reservoirs, however, are relatively modern advancements in water supply management, developing in response to growing populations and the need for safe, reliable drinking water. This system allows for extensive infrastructure and resources to treat and distribute water across broader areas, which was not feasible or necessary in earlier societies that typically relied on nearby, untreated sources.