Greywater still can serve many useful purposes, depending on how clean it is, and what type of cleaning processes you would like to put it through. The easiest solution is to use it in situations where it will become blackwater, such as for flushing your toilet, but with some light filtering it can be used to water your plants and garden and with more extensive filtering it can be re-used for basic hygiene and even become potable again.
It is easiest to fit a house for greywater management during the initial design. This is becoming a much more common practice in Germany as well as in countries where water is scarce. Usual greywater management facilities are composed of 3 sedementation tanks with progressively fine levels of filters. Given a sufficiently large amount of land, these are sometimes also setup as wetparks, consisting of 3 connected ponds with natural filters between them.
The first filter level is usually make of lime gravel. The water will flow through the gravel into the first pond or tank where heavy sediment that made it through the gravel filter will settle to the bottom, the water will then slowly flow into the second tub and then through into the third each time passing through progressively smaller filters (often sand and sometimes charcoal). When a waterpark is used (often for a small community, not just for a single house, though if you have enough land, it could be used for a single house), plants also play an important role in purification, and the process is much slower, usually taking about 1 year for the water to make it's way through the entire system. A wetpark is the most thorough way to reclaim greywater and if done properly can even turn the water potable again.
Some people have also started using living walls with the aim of re-using greywater. A living wall is a vertical garden where plants are rooted in compartments between two sheets of fibrous material anchored to a wall. Water (in this case, greywater) trickles down between the sheets and feeds moss, vines and other plants. Bacteria on the roots of the plants help to metabolize air and water impurities. Active living walls are often joined to a building's air circulating system: Fans blow air through the wall and then recirculate it throughout the building. Living walls can do an excellent job at cleaning up greywater, making it perfect as utility water in your house. They also increase the oxygen levels in the air and can be of particular help in curing sick building syndrome. Plus, they are beautiful to look at!