Consumers and consumer groups are increasingly applying market pressure to improve sustainability in the products they purchase. Additionally, more attention is paid to the ecosystem services of urban forests and landscapes. City planners and community organizations looking for horticultural products to meet these demands represent a market segment that is very aware of water scarcity and sustainability, and they have strict production standards for the products they purchase. Water footprint analysis in nursery crop production is a critical piece of meeting those needs as we move into the future.
Water footprint measures “consumptive use” of fresh water, as defined by
The Water Footprint Network, a global organization started in 2008, addresses the world’s water crises by advancing fair and smart water use. Today, the Water Footprint Network has more than 200 partners from large companies to small suppliers, regulatory bodies, non-profit organizations, and academics. In 2011, they developed a set of methods for assessing water footprint. This international standard for water footprint assessment has broad application, allowing for meaningful and science-based comparison of processes, products, and commodities (Table 1), but also communities and organizations. Furthermore, since it connects consumers to very distant supply chains, it is important to recognize water as a global resource. Put plainly, industrial and agricultural products in the United States are exported to distant markets, making North America an exporter of “net virtual water.”
A water footprint analysis is not meant to be a regulatory stick to beat on consumers or
A water footprint is the sum of four other water footprints (WF): Embodied WF, Green WF, Blue WF, and Grey WF. Embodied WF refers to the water footprint of input materials, including plastics, fertilizers, pesticides, fuels, etc. Green WF refers to the volume of irrigation avoided due to rainfall events. Blue WF refers to rainfall runoff captured or added from surface or groundwater sources (e.g. when one saves rainwater in a reservoir). Grey WF refers to the required volume of water necessary to dilute to public standards any water containing nutrients or pesticides released into a stream, lake, or
Embodied water footprint. The synthesis and fabrication of plastics have a relatively high water footprint. A 1-pint plastic bottle uses 1.4 gallons of water to create. Globally, the grey water footprint required to produce new plastic packaging was 330 billion cubic meters (over 87 trillion gallons) of fresh water in 2016. This is roughly the same amount of water India uses for domestic purposes during a four-year period. The water footprint for each fabricated, consumable component of a marketable nursery plant, including containers, trays, fertilizers, insecticides, and herbicides, are all totaled and represent the embodied water footprint. Unfortunately for producers, the water footprint of these individual components is only referenced in complex databases that are not easily accessible. For reference, preliminary data shows the Embodied WF for a single, marketable #3 container shrub is around 4 gallons.
Green water footprint. Green water is the volume of water from avoided irrigations due to rainfall events (Figure 1). Water captured from rainfall or melted snow does not count towards
Unlike green water, blue water is a weighted water volume. The weighting process reflects the scarcity of water specific to the time of year, geographic location, and the source of water.
Grey water footprint. Grey water refers to the volume of water required to dilute pollutants down to acceptable levels (Figure 2). It is an attempt to quantify the amount of water a pollutant is “using” from the body of water, be it a stream, river, bay, or
Weighting by scarcity
Although the methods of calculating water scarcity are still being discussed by researchers to date, water scarcity is reflected numerically as a ratio or fraction between 0.001 and 100 (Table 2). Lower numbers represent high water abundance while higher numbers represent increased scarcity. The ratio is meant to reflect
The process of weighting consumptive water use is calculated on a per month basis, as withholding or extracting water from a stream has a greater impact during a dry season than a wet one. It is important to note only blue water and grey water are weighted.
Example water footprint analysis
In Figure 3, we see a detailed, weighted water footprint analysis for a single, marketable #3 container holly grown on the East Coast of the U.S. It shows the water footprint of each of the four components (embodied water, green water, blue water, and grey water). It further breaks down the blue water portion to show how the water is consumed by the system, with about 11 gallons being used during irrigation events while almost 8 gallons were lost to evaporation while sitting in the reservoir. Figure 4 and 5 characterize a water footprint of young greenhouse plants between an older overhead irrigation and
Water footprint research and outreach discussed in this article