Which of the following best defines graywater?

Graywater is best defined as water that has been used in household activities such as washing hands, showers, and laundry, but does not include water from toilets, which is considered blackwater. The key characteristic of graywater is that it is relatively clean and can be reused for applications such as irrigation and flushing toilets, making it an important resource in sustainable water management practices.

This definition aligns with the understanding that graywater can still contain some level of contaminants, which is lower than blackwater, hence it can be treated and reused. The other options describe different types of wastewater or water sources that either cannot be reused or are considered more contaminated, which do not align with the proper definition of graywater.