working toward 
sustainability
Is the Water in Your Toilet Too Clean?
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In certain parts of the world, such as the United States, sanitation regulations impose such high standards on household wastewater that we classify relatively clean water from bathtubs and washing machines as contaminated. This water must then be treated as sewage. On the other hand, we use clean, drinkable water to flush our toilets and water our lawns. Can we combine these two observations to come up with a way to save water? One idea that is gaining popularity throughout the developed world is to reuse some of the relatively clean water from bathtubs and washing machines that we normally discard as sewage.
Gray water Wastewater from baths, showers, bathrooms, and washing machines.
Contaminated water Wastewater from toilets, kitchen sinks, and dishwashers.
This idea has led creative homeowners and plumbers to distinguish between two categories of wastewater in the home: gray water and contaminated water. Gray water is defined as the wastewater from baths, showers, bathroom sinks, and washing machines. Although no one would want to drink it, gray water is perfectly suitable for watering lawns, washing cars, and flushing toilets. In contrast, contaminated water is defined as the wastewater from toilets, kitchen sinks, and dishwashers; such water contains a good deal of waste and contaminants and should therefore be disposed of as sewage.
Around the world, there is a growing number of commercial and homemade systems used for storing gray water to flush toilets and water lawns or gardens. For example, a Turkish inventor has designed a household system allowing the homeowner to pipe wastewater from the washing machine to a storage tank that dispenses this gray water into the toilet bowl with each flush.
Many cities in Australia have considered the use of gray water as a way to reduce both the consumption of fresh water and the volume of contaminated water that is sent to sewage treatment plants. The city of Sydney estimates that 70 percent of the water used in the greater metropolitan area is used in households, and that perhaps 60 percent of that water becomes gray water. The Sydney Water Corporation, provider of water services to metropolitan Sydney, estimates that the use of gray water for outdoor purposes could save up to 50,000 L (13,000 gallons) per household per year.
Unfortunately, many local and state regulations in the United States and around the world do not allow households to use gray water. Some localities allow the use of gray water only if it is treated, filtered, or delivered to lawns and gardens through underground drip irrigation systems to avoid potential bacterial contamination. Arizona, a state in the arid Southwest, has some of the least restrictive regulations. As long as a number of guidelines are followed, homeowners are permitted to reuse gray water. In 2010, in the face of a severe water shortage, California reversed earlier restrictions on gray water use and agreed to allow gray water to be used for irrigating lawns and trees. Given that the typical household in the United States produces 227,000 L (60,000 gallons) of gray water annually, using gray water for irrigation presents a major opportunity for water conservation.
Critical Thinking Questions
Given that gray water can contain more bacteria than clean water, how should we balance a desire to irrigate with clean water against the need to conserve limited water supplies?
After reading the two references listed below, describe how you could formulate an argument to convince a town council to permit the use of gray water for watering lawns.
References
California Gray Water Guide. http:/
Grey Water Action. http:/