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Introduction
There is an increasing awareness that water resources exist in limited quantities, and available supply varies considerably during the course of a year. As a result, there is an urgent need to find ways of saving, reusing and recycling water and to develop methodologies to improve water resource management. One long-term strategic goal advocated by several authorities is developing a stable supply of water throughout the year. This goal is consistent with a change in water resources management, which traditionally focused on supply-side policies. In fact, from the 1970s a movement toward demand-control policies has been challenging the expansion of supply capacity to meeting growing needs (Hiessel, 2002). The simultaneous emergence of these goals and paradigms of sustainable water management facilitates the development of constructive applications of new technologies to address these issues.

Demand Control Policies
Demand control policies, however, require that water supply agencies establish complete, accurate, and representative information about current water consumption patterns. A realistic assessment of regional water consumption is essential in understanding how water suppliers can accommodate variations in time and type of use. Consumption patterns include a number of water use characteristics representative of the individual users in space and time. These characteristics include, but are not limited to: the number of inhabitants to be supplied with water and their demographics; the consumption habits of the population; the type of development, property size; and property landscape. Each of these (and several other) parameters play a role in explaining overall demand. However data limitation have precluded analysis of the effects that these variables play. Municipalities have relied upon analysis of large-scale consumption patterns to evaluate management options (Forster, 1979; Martin, 1994; Gracia, et. al., 2001). Municipal water managers today are attempting to understand better the general patterns associated to water use in the supply region. Once identified, municipal water suppliers can curtail demand by evaluating alternative demand-oriented management options tailored specifically to those areas. In this paper we propose a methodology that utilizes a Geographic Information System (GIS) and empirical data for analyzing spatial water consumption patterns with the objective of prioritizing water conservation areas within the City of Seattle, Washington (USA). While the proposed method is applicable to one city, namely, Seattle, we foresee application to any city that has the appropriate data. The raw data are publicly available, provided by the City of Seattle and the National Oceanic and Atmospheric Administration (NOAA).

Although Seattle is currently developing a comprehensive water supply plan for the coming decade, the City has been exploring conservation strategies aimed at curbing water demand in the near future. One of these strategies gaining considerable interest across the city involves the installation of rainwater capture systems that harvest rainwater from the roof, and channel it into a storage device (Figure 1). In essence, the proposal consists of capturing rainwater from rooftops during the winter months, storing through spring, and using for all non-potable purposes during high-demand summer months. While this technology is by no means new, the capital investment to install rainwater catchments at each household across the city is formidable. Therefore, there is widespread concern that such strategies need simultaneously to target areas with highest potential for conservation, keep costs minimal, and, ideally, reduce the ecological impacts associated to storm-water flows.

The following paper develops a spatially explicit methodology for assessing the potential application of rainwater catchments in the city of Seattle. The methodology aims to address the question, which parcels within the city have the highest overall potential for water conservation using rainwater capture systems? Seattle Public Utility (SPU), the primary water supplier in this region, expects to use the results of this study to begin a pilot rainwater capture project targeted at the highest conservation areas, and, subsequently assess the efficacy of the project. If successful, the Utility proposes applying rainwater-harvesting systems across all parcels in the city.

It is important to emphasize that this study does not examine the role of price or householder's characteristics on water demand; rather it examines water use patterns at a specific time in priority areas of the city. The intention of this paper is to develop a GIS based methodology upon which householder characteristics can later be incorporated. Moreover, this study is the first piece of the rainwater catchment assessment, namely, the identification of households within specified areas with highest potential for water conservation. There are three parts to this paper. The first section, describes the study area, data and methods; second, we use statistics and the GIS to evaluate results; and last, we provide recommendations for refining this analysis so that water managers can apply this methodology at the city scale.

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