Abstract: A rainwater harvesting device and system that stores water for irrigation and outdoor use that provides constant pressure via gravity to a sprayer such as might be used for landscape or garden irrigation, or outdoor washing. The device and system comprise a water storage vessel that is free to move vertically, and optionally contained within a rack or other structure if necessary, and supported by one or more springs, which can be compression or tension springs or a combination thereof. When the vessel is at or near capacity, the spring assembly is largely or fully compressed/extended and supports the vessel at a minimal elevation. In such a state, the pressure head provided by the static water level is sufficient to provide a desired pressure at the sprayer.