hemelwater

Hemelwater is a Dutch term that literally means water from the sky, most commonly referring to rainwater. In everyday use, it denotes precipitation that can be collected or managed for various purposes, and it is distinguished from groundwater, surface water, or tap water. The concept is widely used in hydrology and water management within Dutch-speaking contexts to describe rainfall that falls on roofs, streets, or other surfaces and may be captured for storage.

In modern water management, hemelwater is often handled separately from wastewater to reduce stormwater runoff and sewer overflows. Rainwater harvesting systems collect hemelwater from roofs and store it in tanks or cisterns for later non-potable uses such as toilet flushing, irrigation, laundry, and cleaning. The suitability of rainwater for potable use depends on treatment and local regulations; untreated rainwater can contain particulates, microorganisms, or pollutants from catchment surfaces.

Quality and treatment considerations vary by climate and catchment materials. While rainwater can be relatively clean, it may require filtration and disinfection to meet health and safety standards for non-potable use or, in some cases, potable use with appropriate treatment. Many jurisdictions have guidelines or standards for rainwater systems and encourage their installation as part of sustainable urban drainage and water conservation efforts.

See also: rainwater harvesting, stormwater management, sustainable urban drainage, non-potable water reuse.