Given the growing water shortages worldwide, there has been increasing interest in reusing gray water, the water that drains from sinks, bathtubs and washing machines. While gray water is not suitable as drinking water, it can be used for agricultural and landscape watering and a number of different systems -- from high-tech to do-it-yourself -- have been designed for that purpose.
The main advantages of reusing gray water are the cost savings that come from reduced water use, as well as the satisfaction derived from preserving a precious natural resource. However, whether it makes sense for a household to reclaim its gray water depends in part on the climate of the surrounding area. People who live in regions with high average rainfall and few water shortages can collect rainwater to water their back yards during dry spells, a process that is simpler than setting up a gray water reclamation system and offers the same benefits.
However, homes in regions such as the southwestern United States, where droughts are frequent, could greatly benefit from more gray water reclamation. In many areas, outdoor watering makes up more than half of a residence's water use [source: BASIN]. Diverting some of that indoor water to the outdoors not only saves money but can also mitigate water shortages. Re-using gray water also helps the efficiency of septic systems by funneling less water to them, which ultimately extends the life of those systems.
Because of gray water's less-than-pristine state, however, there are some disadvantages to using it. Although gray water is clean compared to toilet water, it can contain any number of chemicals that can be harmful to humans and animals if ingested. Chemicals in shampoos or hair coloring, bacteria from dirty hands, grease and oils can all come down through sink drains, and those materials can potentially damage the plants they come into contact with. For that reason, gray water should be directed directly into the ground (where the soil will naturally filter out any harmful ingredients) rather than being sprayed onto branches or leaves.
Gray water never should be used where it might come into direct contact with human skin. That means it's not recommended for watering lawns, scrubbing decks or cleaning off patio furniture. Furthermore, because it contains a mix of chemicals and organic matter, it should never be stored for more than 24 hours. Rainwater, on the other hand, can be held in reserve far longer, if stored properly.
Gray water is used household water that is dirty but does not contain fecal matter or other dangerous contaminants. While not fit for drinking, this "gray" water can be used for many household purposes, such as watering gardens. The advantages of reusing gray water include financial savings on water and sewage bills. Plus, the nutrients that can be found in gray water (like nitrogen, phosphorous and potassium) can be sustaining for plant life and soil. The downsides to reusing gray water include the extra effort needed to maintain the process, and a chance that mismanaged water will contaminate or pollute your property. Also, gray water can be dangerous to kids and pets. The other potential disadvantage to reusing gray water is that if the water that normally washes waste to sewage treatment plants is diverted, less water will be cleaned and reintroduced into your local plumbing system.
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