Irrigation is the most common application for harvested water. Treatment requirements are lower, which makes the harvesting system simpler, and the demand can quickly drain the cistern to make room for the next storm event. However, relying solely on irrigation for net-annual runoff reduction is rarely enough. In most locations, there is significant rainfall and irrigation is unnecessary. The Pacific Northwest and Southern California, for example, have the majority of rainfall in the winter when there is no irrigation demand.
To get meaningful runoff reduction on a net annual basis, engineers will need to find additional applications beyond irrigation. Other possible applications may include:
2. Toilet Flushing
Creates year round water demand. Multi-story buildings increase the number of toilets under the rooftop and create more demand than irrigation for denser developments.
3. Washing Machines
After toilet flushing, washing machines create the most non-potable demand in residential applications. Harvested water, if treated appropriately, can be used as the source of cold water for washing.
4. Hose Bibs and Outdoor Washing
Many commercial, industrial, and government buildings perform outdoor washing operations that are well suited for harvested water. Vehicle washing, window washing, and cleaning of photovoltaic solar cells are common examples.
5. Process Water
Commercial or industrial projects may have water-intensive processes. Cooling water is required for many industrial operations and can represent a large, steady demand for harvested water.
6. Potable Applications
Potable applications are not practical for most projects where runoff reduction is the goal. Demand is a small portion of the water budget; treatment costs are higher and monitoring is required to meet drinking water standards.