ISO 14046 water footprint: withdrawn water is not consumed water
Counting litres is not a water footprint. Scarcity weighting, the consumption-versus-degradation split, and regional sensitivity.
By clca Editorial TeamLast updated
A water footprint is a structurally different indicator from a carbon footprint, and that difference is routinely overlooked. A tonne of CO₂ has the same climate effect wherever it is released. A cubic metre of water has a completely different effect depending on where it is taken: a cubic metre in Norway is not the same as a cubic metre on the Konya Plain.
Withdrawal, consumption and degradation
ISO 14046 separates three concepts. Withdrawal is the total volume taken from the system. Consumption is the volume taken that does not return to the same catchment — through evaporation, incorporation into the product, or discharge to another catchment. Degradation is the change in quality of the water that does return.
A calculation that skips this distinction overstates the footprint of a plant using cooling water by several times: withdrawal is large but almost all of it returns to the same catchment. Conversely, a process that binds water into the product or evaporates it creates far greater impact from far smaller volumes.
Scarcity weighting
To measure the impact of water use, consumed volume is weighted by the water scarcity of the catchment it came from. The AWARE method was developed for this: it produces a characterisation factor from the water remaining in a catchment after ecosystem and human demand are deducted.
- The same volume can carry tens of times more impact in a scarce catchment
- Catchment-level data is needed; a country average is usually insufficient
- Seasonality matters — summer withdrawal carries different weight from winter
- Groundwater and surface water have different replenishment rates
- Supply-chain water is usually far larger than on-site water
Why the last point matters
A textile mill's own water consumption is small beside the irrigation water in the cotton it uses. Likewise, most of a food business's water footprint sits in agricultural inputs. A water calculation looking only at the site boundary misses most of the impact.
Water indicators in EN 15804
EN 15804+A2 reports two different water-related indicators. Net fresh water use appears in the resource use section as an inventory indicator, while a scarcity-weighted indicator appears in the impact assessment section. Confusing the two is a common error when reading EPDs.
Tags
- water footprint
- ISO 14046
- impact categories
- scarcity weighting
- regional data
- EN 15804
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