Explanation
Rainwater is the type of water that would be most useful for landscape irrigation when considering water conservation and water efficient landscaping. Rainwater is water that falls from the sky as precipitation, and it can be collected and stored in tanks, barrels, cisterns, or ponds for later use1. Rainwater is a renewable and free source of water that does not require any treatment or pumping, unlike potable water, which is water that is safe for human consumption and often comes from municipal sources2. Potable water is a scarce and valuable resource that should be conserved for drinking, cooking, and hygiene purposes, rather than for irrigation2. Clean water is a vague term that can refer to any water that is free of contaminants, but it does not necessarily mean that it is potable or suitable for irrigation3. Blackwater is water that contains human or animal waste, such as sewage or toilet water, and it poses a health and environmental risk if used for irrigation without proper treatment4. Therefore, rainwater is the best option for landscape irrigation, as it reduces the demand for potable water, lowers the utility bills, and benefits the plants and soil1.
References:
Rainwater Harvesting for Landscape Irrigation
Potable Water
Clean Water
Blackwater