From where is the water inlet supply to a localized water heater typically drawn?

The water inlet supply to a localized water heater is typically drawn from the cold mains. This is because localized water heaters, such as tankless or point-of-use heaters, are designed to heat water on demand and rely on the pressurized cold water supply provided by the municipal water system.

Using cold mains ensures a consistent and adequate flow of water, which is essential for the proper functioning of the heater. The mains supply provides fresh and often treated water directly from the city's water treatment facilities, ensuring quality and reliability.

In contrast, rainwater collection systems, hot water cylinders, and storage tanks are generally not used as direct sources for localized water heaters. Rainwater systems may be used for various applications, but they are less common in residential hot water systems due to variability in supply and quality. Hot water cylinders contain pre-heated water and would not serve as a source for the inlet since localized heaters operate differently. Similarly, while storage tanks can be associated with some heating systems, they usually serve as a reserve for larger systems rather than as the immediate source for a localized heater's hot water supply.