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Indicators in Practice

Jan 21, 2015

The Nature Conservancy's Urban Water Footprint

TNC's Urban Water Blueprint provides information for 534 cities and 2000 watersheds.

3.9 billion people currently live in cities of 500,000 inhabitants or more. By 2050, that number will increase to 6.4 billion. Many of these big cities have yet to be built.

These numbers represent a huge opportunity to design and implement policies and best practices to ensure efficient and equitable consumption of natural resources. In the Urban Water Footprint Report, The Nature Conservancy, in partnership with C-40 Cites for Climate Leadership and The International Water Association, attempts to demonstrate the market potential for conservation-based approaches to improve water services and outcomes for the world’s largest cities.

Case Study: Urban Water Footprint

Scope: Global (534 cities, 2000 watersheds)

Released: 2014

Intended Audience: General public; city governments; utilities

Potential Application:  Urban and watershed management

Developer: The Nature Conservancy in partnership with C40 and the International Water Association


Many city dwellers do not have an accurate sense of where their water comes from, and how much there is. Increasingly, it is the case that cities avoid water scarcity through importation or by investing in expensive technologies (e.g., desalination), creating a false sense of security.

The Nature Conservancy's Urban Water Footprint map, published in mid-November 2014, has multifold uses. It increases civic awareness on urban water quality and quantity, acts as a water risk management tool for urban water policy and management, and highlights the potential for conservation-based solutions. The interactive map uses indicators (Figure 1) such as average distance to water resources, percentage of interbasin transfer, and mix of water resources (desalinated, surface, and groundwater), to create a risk profile and to demonstrate the cost vs. benefit of different conservation-based solutions. The map allows for comparative analysis by also including information on which cities are most alike in terms of their risk profile and suggested solutions.

Featured cities profiles include a brief history of the city’s water management practices. The map data is accompanied by an 80-page report outlining conservation-based strategies for water management, which TNC demonstrates are more cost-effective than traditional solutions.

Figure 1: Buenos Aires, Argentina, transfers water an average distance of 120km, one of the longer distances in the dataset.

Two hydrological models, WaterGAP, the Water Balance Model (WBM), and data on groundwater footprint (from 2000), were used to determine levels of ground and surfacewater scarcity. Utility data was used to provide a measure for urban water infrastructure's effect on water supply. The dataset is the first of its kind to take into consideration cities' interbasin transfers; the result is a more accurate picture of urban water scarcity. Sedimentation and nutrient-loading were measured using a variety of models and compared with the SPARROW dataset, which is modeled using direct stream measurements from 3,500 sites in the US. While the authors were interested in water quantity and quality metrics for cities with populations greater than 750,000, they were constrained by limited access to water data and poor data, an urgent problem

Figure 2: Parts of the western United States are in a state of severe water stress.

Conservation-Based Strategies for Water Management

The report highlights that water consumption is currently outpacing population growth by 2.6%. A majority of cities (75%) has been able avoid water stress by building infrastructure to import water through interbasin transfers, but this is a short-term solution. Income plays a huge role in cities’ abilities to make such infrastructure investments. The report notes a stark contrast between the geographic patterns of water consumption between wealthier and poorer cities.

While the top wealthiest quartile imports 9.9 cubic kilometers per day to supplement 5 cubic kilometers of local water consumption, the bottom poorest quartile transfers 6.1 cubic kilometers per day to supplement 3.6 cubic kilometers of local water consumption. As most of the growth in urbanization will come from emerging economies, it will be increasingly unlikely for cities to avoid water stress through interbasin transfers. And for now, alternatives to water importation, such as desalination, are extremely cost-prohibitive and energy intensive.

To lessen cities’ dependence on imported water or a press for desalination, the Nature Conservancy proposes 5 conservation-based solutions:

  • reforestation of pastureland,
  • forest protection,
  • agricultural best management practices (BMPs),
  • riparian restoration (river bank restoration),
  • and forest fuel reduction (controlled fires and forest thinning).

TNC believes these conservation-based strategies are much more cost-effective than the engineered solutions for water treatment employed by cities currently. Their performance metric is the reduction of sediment and nutrient (nitrogen and phosphorous) in water supply for human consumption.

To illustrate cost-effectiveness, the group estimates that a 10% reduction in sediments and nutrients (nitrogen and phosphorous), would lead to a 5% reduction in water treatment operating and maintenance (O&M) expenditures, amounting to global cost-savings of $890 million a year. These estimates do not include ancillary benefits provided by these solutions, including increased biodiversity and economic development. To further highlight the financial viability of these strategies, the report points out that while traditional capital expenditures for water treatment and supply depreciate over time, conservation capital appreciates.

Market Viability

Despite these cost-savings and ancillary benefits, the report’s ROI analysis shows that only 1 in 4 cities would profit from implementing the recommended strategies. Also $890 million a year in savings globally diffuses to a miniscule number at the city level. For this reason, the TNC report highlights the need for monetization of conservation benefits through “water funds” and water markets.

Water funds pool monies from from competing users of water, to invest in upstream conservation, to eliminate the need for water treatment. They vary greatly in structure, but generally allow for a more collective approach to municipal water management planning. Water markets have been operationalized nationally in Australia and also in San Diego, California, where farmers are paid twice the municipal water rate for water conserved as a result of more efficient in their agricultural practices.

Conservation-based water management strategies and water funds have a high potential to positively transform urban water management. However change will not be possible without raising civic awareness. Most city dwellers are unaware of their water situation as it relates to scarcity, sourcing, quality, and as a result, don’t regularly engage policymakers on adoption of conservation practices. As cited in the report, confusion still remains as to how cities should navigate regulation and implement the proposed practices.

Exacerbating low civic awareness is the consistent practice of inadequately charging for water. A case in point are the relative rates of water usage and water tariffs in San Diego and Amsterdam. Although San Diego is water stressed (needing to import 100 million cubic meters a year), its per capita water consumption is still 5 times that of Amsterdam’s, which happens to have the world’s 3rd highest water tariff rate.

The creators of the Urban Water Footprint know their interactive map represents a colossal data mining and visualization effort that could prove to be a great tool for increasing civic awareness. The report does a great job presenting the risks to water quality, quantity, and equity posed by not adopting conservation strategies. It provides a practical roadmap for municipalities to think innovatively about water conservation. Hopefully with the Urban Water Footprint Report in hand, urbanites can lead the way in rethinking water in 2015 and beyond.