Gray water, which is also called sullage, is used water that goes down the drain in your kitchen and bathroom. Gray water includes water from sinks, showers, washing machines, and dishwashers, but not toilets. This wastewater can be used more efficiently in two ways: by recycling it in the yard and garden or by sending it back to the bathroom to flush the toilet.
Nowadays, recycling gray water for use on plants and crops is quite easy. The normal method is simply to redirect the water to the yard. There are systems which are designed specifically to move gray water. These systems can be as easy as running a hose from the dishwasher out a window to the yard, or they can be engineered as part of the plumbing system in the house.
There are also methods to clean the water, such as sand filtering and treatment ponds. Cities have different rules about how gray water allowed to be used. In general, the most common regulations include not storing this water for more than a day and not allowing it to form pools or spread and run off the surface of the property.
In most regions of Europe and Australia, using gray water inside the house to flush toilets is common. The primary advantage of recycling gray water in this way is that household water use can be reduced by an average of 30 percent. However, it's important to note that laws detailing how long the water can be stored (usually one day) are strictly enforced.
【題組】33. Which of the following words does not have the meaning of “sullage”？
(B) filtered water
(C) gray water
(D) used water