Can We Put a Value on Water Purification?

Valuation of ecosystem goods and services need not be limited to monetary notions. The value of the services can include esthetic, biological, recreational, and health benefits. Monetary valuation can, however, be helpful in identifying tradeoffs among competing uses of an ecosystem, as well as provide a way to bring attention to the broader spectrum of benefits. In reality, it is difficult to attribute a monetary value to the services provided by natural ecosystems. There are many hidden benefits or tradeoffs that make it hard to evaluate and easy to underestimate the true value of any particular service. Philosophical and ethical questions are inherent in monetary valuation (12). Nevertheless, there is a growing interest in developing methods to provide an economic perspective on the value of ecosystem services (see 12,3,18,4). Some of the ways of valuing ecosystem services are described below.

Replacement Cost
One approach is to estimate the cost to replace a desired service if it is lost. This is a common method used in deriving an economic value for water purification services. In New York City, for instance, the replacement cost for the water purification services once provided by its now-contaminated watershed was estimated at $6 to $8 billion in capital costs for the installation of an artificial filtration plant, plus annual operating costs of $300 million. On the other hand, the cost of restoring the integrity of the watershed, and thus the purification services, was estimated to be approximately $1 billion. The restoration includes costs to purchase and halt development on land in the watershed, to compensate landowners for restrictions on private development and to subsidize the improvement of septic systems (20). It is important to note that the replacement cost does not include any estimate of the value of other services such as flood control, carbon sequestration, maintenance of biodiversity or personal enjoyment, that the watershed restoration will enhance.

Wastewater Treatment
Another way to look at the value of the purification service provided by aquatic systems is to consider the situations in which we have tried to capitalize upon the natural process, or tried to mimic it. Over the last two decades, the use of natural wetlands for tertiary wastewater treatment has become popular, particularly in small communities. Several hundred wetlands in the United States and Canada are used for wastewater treatment (7). Recently however, the economic and social costs of discharging wastes into natural systems have become more clear. Wastewater discharge into a wetland can lead to dramatic changes in plant and animal species and composition. Contamination of surface water and groundwater has been a problem and will increase as human populations grow (7). The impact on other services, such as wildlife habitat and discharge of water into other downstream ecosystems is a risk. One alternative that has been under exploration for some time is the construction of new wetlands for wastewater treatment.

Constructed Wetlands
Constructed wetlands have been developed to mimic some natural wetland functions. There are at least three classes of constructed wetlands: (17) those constructed as alternative wastewater treatment facilities; (13) those used to mitigate for destruction of natural wetlands, and; (5) those used for wildlife enhancement (particularly waterfowl). Constructed wetlands have been developed to mimic some of the known filtration power of natural systems and in some situations can be a cost-effective and environmentally sensitive alternative to other means of treating wastewater. They are useful where more traditional water treatment methods do not work, for example in areas of high water table or very shallow soils, and can be cost efficient for small communities, especially those that can't afford wastewater treatment plants. They may also be especially useful in areas with degraded wetlands, or surface-mined areas, and to treat agricultural runoff or other non-point sources of pollution (7). However, constructed wetlands do not have the history of substrate development and subsurface water movement that natural wetlands do, and should not be expected to substitute for natural wetlands.


Chemical Cleaners
In general, we rely on wastewater treatment plants as the final step in cleaning water after we use it. Water purification technology is costly. In the case of drinking water, the more polluted the water the more money is needed for disinfectants, such as chlorination, and the higher the energy, equipment, and labor costs.

There are also health costs associated with degraded water quality. Wetlands can play a major role in the removal of pathogens such as E. coli and salmonella (24). More than 100 types of human pathogenic viruses may be present in fecal-contaminated waters (9). Giardia, an intestinal parasite that is difficult to remove from source water, is found in waters receiving urban pollution. Higher concentrations of Giardia and Cryptosporidium have been found in waters receiving industrial and sewage effluents than in waters not receiving these effluents or having more extensive watershed protection practices (13,9). The use of disinfectants such as chlorine and algaecides such as copper sulfate, can pose a health threat to humans and aquatic organisms. Once waters that contain these substances are discharged back into rivers and streams, they can be harmful to aquatic organisms or even humans. For example, trihalomethanes, a byproduct of chlorination, are potential human carcinogens (13).


Recreation/Quality of Life
Quality of life benefits as well as economic benefits from recreational use can be attached to clean water. More than half of all U.S. adults hunt, fish, birdwatch, or photograph wildlife. These activities add billions of dollars to the national economy annually (6). In 1996, for example, an estimated 37 billion dollars was spent in the U.S. on fishing-related expenditures (25).

The drinkable water supply for a large percentage of the population in the United States comes from watersheds that are protected to some degree. Over half of the human population in the western United States derive water supplies from National Forest watersheds which are managed by the U.S. Forest Service. (23)