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In urban settings, the one-time use of water to disperse human and industrial wastes is becoming an outmoded practice, made obsolete by new technologies and water shortages. Water enters a city, becomes contaminated with human and industrial wastes, and leaves the city dangerously polluted. Toxic industrial wastes discharged into rivers and lakes or into wells also permeate aquifers, making water—both surface and underground—unsafe for drinking. And their toxic wastes are destroying marine ecosystems, including local fisheries. The time has come to manage waste without discharging it into the local environment, allowing water to be recycled indefinitely and reducing both urban and industrial demand dramatically.
The current engineering concept for dealing with human waste is to use vast quantities of water to wash it away, preferably into a sewer system where it will be treated before being discharged into the local river. The “flush and forget” system is expensive, water-intensive, it disrupts the nutrient cycle, and it is a major source of disease in developing countries.
As water scarcity spreads, the viability of water-based sewage systems will diminish. Water-based sewage systems take nutrients originating in the soil and typically dump them into rivers, lakes, or the sea. Not only are the nutrients lost from agriculture, but the nutrient overload has led to the death of many rivers and to the formation of some 200 dead zones in ocean coastal regions. Sewer systems that dump untreated sewage into rivers and streams are a major source of disease and death.
Sunita Narain of the Centre for Science and Environment in India argues convincingly that a water-based disposal system with sewage treatment facilities is neither environmentally nor economically viable for India. She notes that an Indian family of five, producing 250 liters of excrement in a year and using a water flush toilet, requires 150,000 liters of water to wash away its wastes.
As currently designed, India’s sewer system is actually a pathogen-dispersal system. It takes a small quantity of contaminated material and uses it to make vast quantities of water unfit for human use, often simply discharging it into nearby rivers or streams. Narain says both “our rivers and our children are dying.” India’s government, like that of many other developing countries, is hopelessly chasing the goal of universal water-based sewage systems and sewage treatment facilities—unable to close the huge gap between services needed and provided, but unwilling to admit that it is not an economically viable option. Narain concludes that the “flush and forget” approach is not working.
This dispersal of pathogens is a huge public health challenge. Worldwide, poor sanitation and personal hygiene claim 2.7 million lives per year, second only to the 5.9 million claimed by hunger and malnutrition.
Fortunately, there is a low-cost alternative: the composting toilet. This is a simple, waterless, odorless toilet linked to a small compost facility. Table waste can also be incorporated into the composter. The dry composting converts human fecal material into a soil-like humus, which is essentially odorless and is scarcely 10 percent of the original volume. These compost facilities need to be emptied every year or so, depending on design and size. Vendors periodically collect the humus and can market it as a soil supplement, thus ensuring that the nutrients and organic matter return to the soil, reducing the need for fertilizer.
This technology reduces residential water use, thus cutting water bills and lowering the energy needed to pump and purify water. As a bonus, it also reduces garbage flow if table waste is incorporated, eliminates the sewage water disposal problem, and restores the nutrient cycle. The U.S. Environmental Protection Agency now lists several brands of dry toilets approved for use. Pioneered in Sweden, these toilets work well under the widely varying conditions where they are now used, including Swedish apartment buildings, U.S. private residences, and Chinese villages.
At the household level, water can be saved by using showerheads, flush toilets, dishwashers, clothes washers, and other appliances that are more water-efficient. Some countries are adopting water efficiency standards and labeling for appliances, much as has been done for energy efficiency. When water costs rise, as they inevitably will, investments in composting toilets and more water-efficient household appliances will become increasingly attractive to individual homeowners.
Two household appliances, toilets and showers, together account for over half of indoor water use. Whereas traditional flush toilets used 6 gallons (or 22.7 liters) per flush, the legal U.S. maximum for new toilets is 1.6 gallons (6 liters). An Australian-produced toilet with a dual-flush two-button technology uses only 1 gallon for a liquid waste flush and 1.6 gallons for a solid waste flush. Shifting from a showerhead flowing at 5 gallons per minute to a 2.5 gallons-per-minute model cuts water use nearly in half. With washing machines, a horizontal axis design developed in Europe uses 40 percent less than the traditional top-loading models. In addition, this European model now being marketed internationally also uses less energy.
For cities, the most effective single step to raise water productivity is to adopt a comprehensive water treatment/recycling system, reusing the same water continuously. With this system, only a small percentage of water is lost to evaporation each time it cycles through. Given the technologies that are available today, it is quite possible to recycle urban water supplies comprehensively, largely removing cities as a claimant on scarce water resources.
Some cities faced with shrinking water supplies and rising water costs are beginning to recycle their water. Singapore, for example, which buys its water from Malaysia, is beginning to recycle water, reducing the amount it imports. For some cities, the continuous recycling of water may become a condition of their survival.
Individual industries facing the same water-related issues as cities are beginning to move away from the use of water to disperse industrial waste. Some companies segregate effluent streams, treating each individually with the appropriate chemicals and membrane filtration, preparing the water for reuse. Peter Gleick, senior author and editor of the biannual report The World’s Water, writes: “Indeed, some industries, such as paper and pulp, industrial laundries, and metal finishing, are beginning to develop ‘closed-loop’ systems where all the waste water is reused internally, with only small amounts of fresh water needed to make up for water incorporated into the product or lost in evaporation.” Industries are moving faster than cities, but the technologies they are developing can also be used in urban water recycling. The existing water-based waste disposal economy is not viable. There are too many households, factories, and feedlots to simply try and wash waste away on our crowded planet. To do so is ecologically mindless and outdated—an approach that belongs to an age when there were many fewer people and far less economic activity.
Adapted from Chapter 11, “Designing Sustainable Cities,” in Lester R. Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble (New York: W.W. Norton & Company, 2006), available for free downloading and purchase at www.earth-policy.org/books/pb2.