An Industrial Water Impact Index case study - Veolia Water Solutions ...

The Water Impact IndexVOLUME• Water Quality• Volume ofwater used –withdrawn andreleased+STRESS• The Water StressIndex• Local conditionof resource+QUALITY• Water quality –withdrawn andreleasedbe used to support decision-making and communication,among other uses. The result of Veolia’s effort is theWater Impact Index, a comprehensive water footprintindicator that integrates all aspects of the water cycle,including water quality and availability in the localenvironment.With the Water Impact Index, the physical water quantitybalance for any product or process is weighted by a qualityindex and a water stress index, as seen above. The waterquality index provides a means of measuring changesin water quality and the value of water treatment. Thewater stress index accounts for the level of stress onthe resource. Together these factors, through the WaterImpact Index, provide a means of measuring the full waterimpact. Indirect impacts from the production chain suchas water use from energy, raw materials, chemicals, andwaste generation are also incorporated into the balance.The methodology is elegant in its simplicity. In essence,the Water Impact Index is a mass balance equation thatcompares the quantity, quality, and stress factor of thewithdrawn water to the same parameters of the releasedwater (see below). The equation multiplies the threevalues of volume, stress index, and quality index in thewater volume withdrawn, and then subtracts the productof the same three factors for the water volume released.There are several key points to realize in the mathematics.First, the quality index is based on a component ofconcern and the same one is used on both sides ofthe equation. Cref is a reference concentration for thiscomponent. It corresponds to the concentration thatshould be reached to ensure protection of the localwater resource for its intended uses. C is the actualconcentration of the component in the withdrawn orreleased water. Second, the stress index is a dimensionlessvalue between 0 and 1 that reflects the local scarcity ofwater. The stress index takes into consideration localwater use and availability, seasonal variations in freshwater availability and storage capacity. These values havebeen mapped for most of the world by Pfister, Zurichin 2009.The Water Impact Index is expressed in gallonsequivalent. This is a mathematical representation of thethree parameters and is not a true gallon of water. Whilethis concept can appear abstract at first, it provides anoptimal tool for decision making purposes. The lower theIndex, the lower the impact to local water resources.A negative value implies that the process benefitslocal water resources. The Index can also be convertedback to actual gallons. Using this information, the userof the tool has an idea of what needs to be addressed tolower the impact.To provide the user with a better understanding of thetool, the following characteristics of the Water ImpactIndex are provided.• An increase in the volume withdrawn increases theIndex• An increase in the volume released decreases the Index• An increase in the stress index of water withdrawnincreases the Index• An increase in the stress index of water releaseddecreases the IndexWater Impact IndexEquationStress IndexQuality Index∑[WIIX = W x WSI x min [ 1; Cref l]] – j j l [ R x WSI x min [ k k ljC j,l∑k1; Cref l]] C k,lVolume WithdrawnVolume Released4A WHITE PAPER BY VEOLIA WATER