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Greywater, Solution to Water Crisis?

Greywater serves as an alternative source of water for plumbing and irrigation that could mitigate the current excessive demand for clean freshwater.

With populations increasing worldwide, our demand for clean freshwater has also drastically increased as well. Alternative sources of water supply are being examined, and one of these sources is greywater.

Greywater systems allow for the recycle and reuse of grey wastewater. Several nations across the globe have already implemented greywater systems to prevent water shortages from their large demands of freshwater. In addition to water shortages, greywater systems provide an environmental and economical alternative to water treatment plants.

Clearly, there are several advantages – decrease the demand of the dwindling freshwater resource, reduce the need of costly sewage treatment plants, and help us achieve our goal towards sustainable development – in building a greywater system.

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What is Greywater?

Greywater is defined as wastewater generated from domestic activates—such as bathtubs, showers, and sinks; laundry machines; and dishwashers—excluding toilets, which falls under sewage. Unlike sewage, which contains high levels of organic matter and nutrients from urine, feces, and toilet paper, greywater can be recycled and reused in order to conserve freshwater.

Greywater reuse is potentially feasible for irrigation—landscape and recreation; toilet flushing; fire protection; cleaning; commercial air conditioning; construction; and industry. The two most ideal situations in which greywater would be used are irrigation and toilet flushing.

Gardens use 34% of the total household water budget while toilet flushing varies from 29 – 47% in a household. That is a combined 65 – 81% that could be replaced with recycled greywater, thus reducing the need of freshwater. There are sufficient amounts of greywater from baths, showers, and sinks to fill the void of now unnecessary freshwater.

Greywater Safety Issues

However, there are a few concerns on whether greywater is safe to reuse. Greywater could be contaminated from household chemicals and microorganisms, two factors that could potentially lead to health and safety issues with greywater.

Microorganisms—pathogenic viruses, bacteria, helminths, and protozoa—originate from bathrooms (hand washing and diaper changing) to kitchens (raw meats and other spoiled foods). Greywater can also contain a variety of bacteria and other parasites such as E. coli, Salmonella, roundworms, and viruses.

Furthermore, microorganisms found in greywater are not only a danger to humans but also to the environment as they may lead to groundwater and plant contamination as well.

Household chemicals also lead to environmental contaminations. Originating from mostly from detergents, soaps, and oil and grease, household chemicals are toxic and can pose as another danger with the reuse of greywater.

Furthermore, greywater reuse in toilet flushing runs a risk of microbiological contamination, which poses a serious risk to health if contact with people. In addition, greywater also contains undesirable materials—such as hair, lint, and fats—that could potentially clog pipes, which could damage the entire greywater system.

Furthermore, greywater reuse in irrigation can lead to environmental contamination from both microorganisms and household chemicals. Both Eriksson et al. and Christova-Boal et al. propose discovering methods in treating greywater before it should be reused.

Greywater - Solution to Water Crisis
Greywater tower at Arba Minch, Ethiopia By SuSanA Secretariat [CC BY 2.0 ], via Wikimedia Commons

Future of Greywater Uses

Fortunately, methods of successfully reusing greywater have already been put into use worldwide. One of the most successful greywater systems is found in Madhya Pradesh, India, where 3,500 schools have efficient greywater reuse systems capable of treating sufficient amounts of water for toilet flushing, cleaning school floors, and irrigation.

Under this system, grey water goes through three treatment steps:

  1. Absorption of soap;
  2. Filtration; and
  3. Treatment using aeration and chlorination.

More important, the treatment of greywater is very efficient in this system; greywater treatment systems have been serving thousands of Madhya Pradesh students since 2006 with no reported illnesses. Madhya Pradesh demonstrates that greywater systems are highly capable of providing sufficient amounts of greywater for toilet flushing and irrigation.


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