Shape Our Water - Non-Potable Water Reuse Analysis

Seattle Public Utilities - Drainage and Wastewater System Planning

Seattle, WA (2019-2020)

A component of the Shape Our Water Analysis Stage, the goal of this geospatial analysis was to identify which areas of the city show the greatest potential demand for non-potable water, as blocks or neighborhoods with relatively high concentrations of non-potable demand may indicate potential opportunities to explore non-potable reuse systems at the district scale.

Water reuse systems can provide multiple benefits for the communities they serve, such as improved system resilience to service disruptions due to seismic or climate change impacts, diversified water supply, increased infrastructure capacity, deferred capital costs, reduced volume of wastewater requiring treatment, decreased receiving waterbody pollution, conservation of potable water, cost savings for water customers, and other co-benefits (National Blue Ribbon Commission for Onsite Non-potable Water Systems, 2018).

Potential non-potable demand was assessed though geospatial analysis to create two citywide GIS layers:

1. Intensive Water Consumers: Identification of the city’s relevant and most intensive overall water consumers utilizing customer records from SPU’s Water Line of Business;

2. High Potential by Land Use: Identification of land uses likely to have significant nonpotable water demand, as determined through:

-EPA estimates of how water is typically used on various land use types;

-categorizing each type of water use as either one that can be replaced by a non-potable source or cannot;

-determining an appropriate threshold for what level of total non-potable demand should be deemed high or low potential based on esearch;

-utilizing case study research on non-potable reuse applications to estimate non-potable demand for those land use categories not covered by EPA estimates

When displayed together, as shown at right, “Intensive Water Consumers” (blue) and “High Potential by Land Use” (red) reveal the spatial distribution of the City’s intensive water consumers, those with significant non-potable water demand, and those that are both intensive water consumers and have likely high non-potable water demand (purple).

Because clusters of parcels that are both intensive water consumers and have high potential non-potable demand represent the greatest overall opportunity for district scale non-potable reuse systems, the last part of this analysis involved scanning the datasets for “clusters of potential.”

Sixteen clusters were identified, primarily in Urban Centers and Urban Villages, such as those in the Othello and Lake City Urban Villages, shown below. Areas identified as having high potential non-potable demand could be analyzed as opportunities to explore district scale non-potable reuse systems in capacity-constrained areas, where those systems could relieve pressure on the drainage and wastewater system. This analysis could also inform the development of policies or incentives for onsite non-potable water reuse systems at the parcel scale for new development.

As task lead, was responsible for authoring the non-potable reuse technical memo, including conducting the research that informed geospatial analysis decision-making, conducting the geospatial analysis, writing the report, creating maps and graphics, soliciting content review from SPU staff and incorporating feedback. Upon completion, I was responsible for presenting this report to various work groups within the Planning and Program Management division of DWW.