Safe reuse of greywater can be done in what?

Correct answer: Garden irrigation

Greywater is wastewater from relatively light domestic uses, such as handwashing, bathing, or laundry, and it is different from toilet sewage. The governing concept is safe water reuse: greywater must be kept separate from drinking water and used only when local guidance, treatment, and hygiene conditions make the reuse appropriate. Garden irrigation is a common suitable example, especially for ornamental plants and with care to avoid contamination of edible parts. Therefore, option B is correct. Drinking it directly is unsafe, throwing it into an open drain wastes water and may pollute surroundings, and spraying it in a classroom creates hygiene and health risks. Proper handling remains essential.