Water consumption and footwear

John Hubbard, SATRA Technology Centre


Concerns over global warming have ensured that most people are familiar with the concept of the carbon footprint, calculated from the emissions of greenhouse gases during production and transportation and largely linked to the combustion of fossil fuels. A concept that has attracted less attention is that of the water footprint: a measure of the consumption and pollution of water through the manufacturing process.

In many temperate regions of the world water scarcity and conservation has been of relatively low priority on the political agenda, however, for some the allocation, extraction and preservation of water reserves is a critical issue.

Most industrial processes have a water footprint, including footwear manufacture. In comparison to garment making, footwear manufacture is surprisingly complicated, frequently with a large number of materials involved. Whilst there are styles of shoes made from single materials such as plastic sandals these make up only a small amount of the world market. For a typical everyday 'sports' shoe (sneaker), it is not uncommon for this product to contain up to twenty or more materials when uppers, soles, linings, fasteners, reinforcements and foams are all taken into account. Thus the shoe materials supply chain is a highly complex one.

With the onset of ‘globalisation’, the manufacture of footwear moved away from the West to areas where water availability is more acute, either because of climate, lack of infrastructure or general industrial pollution. Most of the world’s shoes are now made in South East Asia, with 60% manufactured in China – predominantly in the South Eastern Provinces of Guangdong, Fujian and Shandong. Although generally not short of water in these areas, previous industrial pollution did cause shortages of safe drinking water and raised significant concerns. In addition, some tanning is also carried out in Africa where limitations regarding water supply can be critical.

Historically, areas of potential pollution associated with the footwear industry have come predominantly from material suppliers where chemical processes during the manufacturer of leather, synthetic materials and textiles and issues relating to the return of extracted waste water has had a negative effect on the environment, rather than from shoemakers themselves. However, many chemical companies and tanners have invested significant resource and effort into reducing the impact of their operations on the environment over the last 30 years or so and, therefore, today’s shoemaking supply chain is significantly more ‘environmentally friendly’ than in yesteryear.

The main impacts of industrial water use are water extraction and water pollution.

Material production inevitably relies on some water extraction from a nearby river or lake. This can impact on the flow or size of the source and also potentially affect flora, fauna and human populations who may rely on that source of water.

After extraction, many industrial processes do not retain the water, often returning it back to the source. In some of the processes that are used in the footwear supply chain (such as tanning of leather, dyeing of textile materials and bleaching and puling of cellulosic materials), the water is not consumed and may be returned to the water supply from which it was taken. In many countries limits are imposed on facilities discharging to public water courses in terms of the presence of harmful chemicals, suspended solids, biological activity as well as temperature and pH. If the post-process water does not meet these requirements then the installation may be required to install some type of water treatment facility.

For most types of footwear (particularly where leather and natural textiles are used), the most demand will be in the rearing/growing and processing of these materials. With respect to the many actual footwear manufacturing processes, whilst they are labour intensive, most are not highly water demanding.

Although small in the grand scale of things, the process of 'heat setting' probably uses the most water during the actual shoemaking phase.

Heat setting is a process by which the shape of the footwear upper is 'fixed' to the shape of the last. This stress-relaxation process was originally achieved simply by storage of the lasted uppers (still on the last) for many weeks. The end of such a time-consuming and last-stock demanding process was welcomed when, in the 1960s, SATRA discovered that the stress-relaxation process could be reduced to mere minutes by exposing the lasted uppers to elevated temperatures and high humidity. Since then, the process time has been reduced still further by utilising high-velocity moist air, although the critical factor, that of high humidity, has remained essential for leather shoes. Although non-leather footwear does not require moisture for adequate setting, in many mixed-production factories it is not practical to differentiate the processes - all are usually treated the same.

Water boilers are required to generate the environment within the heat setter, but with advances in technology both electricity consumption and water usage have been significantly reduced in recent years. In older style heat setters the steam is not recovered - the vapour just escapes to atmosphere at the ends of the heat setting tunnel. However, new designs are being introduced that can condense and recycle the water which should further reduce the new water input required by these systems.

Most water usage arises during the production of the materials from which the footwear is manufactured. Formal, casual and sports footwear still predominantly use leather in the upper. Only the more exotic animals are grown specifically for their hides, and the quantities are insignificant in comparison to the main sources of leather from animals reared for food. So, leather is usually a by-product of the meat and dairy industries. On this basis, it can be argued that the water consumption involved in the rearing of these animals (which includes that used for growing their feed) should not be considered as part of the total water footprint for leather materials. At the very least, a 'reduction factor' should be applied to account for the various end-uses to which the animal carcass is applied.

However, once the hide is taken from the animal, and these are mostly cattle but also includes many goat, sheep and pig skins, then the tanning processes must be considered. These involve many dozens of discrete processes, many of which are water intensive. Tanning is highly demanding and is capable of producing waste water contaminated with toxic and polluting substances such as organic matter, salts, tanning agents and dyestuffs, and has historically been a major potential source of pollution. It is therefore important that tanneries ensure that waste water leaving the facility meets all the requirements for such emissions in the locality. The introduction of new water treatment technology has meant that many tanneries have installed facilities that comply to high standards of water treatment, often significantly reducing any waste water discharges with water being recycled back into the tanning process. This technology has evolved in recent decades and today’s modern tanneries are a world apart from their forebears.

Other natural materials also have significant water demands during their production: wool will require the water for animal raising and feedstock growing. These must here be taken into account because most wool derives from flocks specifically reared for their fleece: meat would be a by-product of these flocks.

Cotton also has an intensive need for water, mainly for irrigation of plants and processing of the fibres: it is estimated that the global water consumption of cotton products is in excess of 250 x 1012 litres (250 trillion litres) of water per year (source: Cotton grows best in warm climates, and worldwide the biggest producers of cotton are China, USA, India and Pakistan. Dryland cotton can be grown in areas of higher rainfall, but most cotton production relies on water irrigation from water sources as natural rainfall is often insufficient.

As with other intensive farming practices, the growing of cotton can also result in the potential contamination of run-off water from pesticides used to protect the crop. Attention to detail and careful application go a long way to minimising the possibility of environmental impact downstream from the cotton growing area. Processing of cotton to produce white cloth will also involve heavy use of water and the use of potential pollutants such as bleaches. To produce coloured materials there are also issues with dyes and auxiliary processing chemicals. Again, industry has made strenuous efforts to recycle and minimise waste water, whilst cleaning up anything discharged. In shoemaking terms the use of textiles is a small proportion of the global cotton market compared to other markets such as apparel and upholstery.

Fortunately with footwear, one life cycle aspect that does not need too much consideration with respect to water consumption is washing. There is only a very small proportion of footwear (mainly textile-based) that is able to be washed and even this would be an infrequent requirement. The laundering phase is a much more important factor when considering the water footprint of clothing and household textiles.

In conclusion, for footwear production the water footprint will be largely associated with the production of any natural and synthetic materials used in the uppers, linings, components and reinforcing materials. Many of these processes have the potential to cause significant pollution if not controlled adequately, and whilst, no doubt, there remain inefficient operations throughout the world, more and more effort is being made towards efficient production processes and new technology means that pollution is largely preventable.

Water resource needs to be taken into account alongside other environmental issues such as the carbon footprint (energy use) and consumer waste at end of product life. Ensuring that all production processes are as efficient as possible and using modern technology to ensure pollution is minimised will ensure industry has a better chance of being accepted by the communities of the regions in which it operates.

For more information on water usage in footwear, environmental auditing, correct operation of heat setters and the many sustainability issues that affect footwear production, please contact the SATRA Research Team.  Alternatively, visit the SATRA website.