Industry is the world's major polluter. Two thirds of the oxygen depletion of surface waters can be traced to industrial wastewater, and nine tenths of their pollution with toxic substances. This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends controlling industrial pollution sources in order to protect water resources.
The biggest pollution problem is linked to small and medium scale industry. Particularly insidious are toxic pollution and persistent substances since these pollutants usually neither smell nor give initially visible impacts. There is a clear linkage to rural development in view of efforts to limit urban migration by expanding employment opportunities in small-scale industry. Rural industry is especially important in over-populated regions where agriculture can no longer absorb the rapidly expanding manpower. In India, this type of industry employs some 17 million people, and in China some 73 million. In China, it represents 56 percent of the country's total gross industrial output value, and in India the sector accounts for 40 percent of the industrial production and 35 percent of the total exports. Small-scale industry in other words represents a fundamental pillar underpinning the socio-economic development efforts in these countries. The small scale of each industrial unit makes water pollution abatement particularly difficult to solve.