Paper

Global average water footprint: 10 litres of water for one A4-sheet of paper.

We assume here eighty-grams paper (80g/m2). Further we assume that the paper is produced from wood. Consider a production forest with an annual evapotranspiration of 600 mm/yr, which is equal to 6000 m3/ha/yr. Suppose that the forest yields 10 m3 of wood per hectare per year. Finally, account for the fact that 1 m3 of wood gives 0.3 ton of paper. This means that the (green) water footprint of paper is 2000 m3/ton (= 2000 litres/kg). Since 1 A4-sheet of paper has a weight of 0.005 kg, this means that 1 A4 has a green water footprint of 10 litres.

On top of these 10 litres come the blue and grey water footprints related to consumption and pollution of water during the paper manufacturing process. The blue water footprint of paper is very small: about 6 m3/ton, which means 0.03 litre for one A4-sheet of paper. This figure mostly refers to evaporation of water used in the milling process; a minor part refers to water retained in process residuals (source: NCASI, 2009). The effluents of paper mills contribute to a grey water footprint when not properly treated before disposal. The figure of 10 litres for one A4-sheet of paper does not include a grey water footprint component, which holds for cases where wasteflows are treated up to standard.

The figure of 10 litres for one A4-sheet of paper obviously varies from case to case, depending on the source of the wood. Particularly, forest evapotranspiration and wood yield vary from forest to forest. The number will likely fall in a range of 2 to 30 litres of water per A4-sheet.