Which of the following is a restriction associated with the use of greywater?

The restriction associated with the use of greywater that is most pertinent is that it must never be sprayed. This is primarily due to health and safety concerns. Spraying greywater can create aerosols, which could potentially allow pathogens and other contaminants present in the wastewater to become airborne, posing a risk of inhalation or spread to areas where they could affect people or animals.

Instead, greywater is generally recommended to be used for subsurface irrigation, such as through drip systems, which minimizes contact with humans and reduces the likelihood of contamination. This guideline is in place to ensure that while greywater can be a sustainable resource for irrigation, it is utilized in a way that safeguards health and environmental quality.

In contrast, the other choices do not accurately represent restrictions on greywater use. For instance, greywater can indeed be used in the irrigation of edible plants with certain conditions, permits may not always be required for reuse depending on local regulations, and it can come from various sources, including kitchen sinks, albeit with some restrictions regarding the types of foods washed and contaminants present.