The Impact of Industrial Water Use on Public Water Supplies

The US Water Resources Council, a cabinet-level group with prime responsibility for coordinating all federally supported water-resources activities, currently is engaged in the Second National Assessment of Water and Related Land Resources. The assessment is concerned with the adequacy of the resources to meet a multitude of demands, both in-stream and off-stream, and the competition among them. It considers not only what the conditions are now, but, more importantly, how they are likely to change over the next 25 years. One of the major concerns is the interrelationship between manufacturing and municipal water supplies. The national assessment projected that the manufacturing gross water demand (the volume of water required if there is no recycling) would increase from 5.82 X 10* mVday (154 bgd) in 1975 to 1.43 X 109 m3/day (378 bgd) ( + 145 per cent) in the year 2000, while actual intake for manufacturing would decrease from 2.6 X 108 m3/day (69 bgd) in 1975 to 8.7 X 107 m3/day (23 bgd) (-67 per cent) in 2000. This latter decrease is of particular concern to those municipal water suppliers who are dependent on the income from industrial users. While municipal water-supply customers include industrial (manufacturing) users as well as commercial and domestic, forecasts of growth and design for expansion of municipal water systems generally combine the three into a per-capita demand alone. The national birthrate has declined to less than replacement level, according to Mar. 1976 reports, but US population growth still has momentum enough, because of the large number of young people, to add 35-50 million more people by the year 2000about a 25 per cent increase. Essentially all of this growth will add to the demand in the service areas of municipal water-supply systems that must expand or develop to accommodate this growth. Growth rates for the manufacturing sector in the projections developed for the Water Resources Council and used in the national assessment are at a much higher rate than that of the population. By the year 2000, if those projections hold, the output of US manufacturers will be 2Vz times larger in the year 2000 than that forecast for 1975. Eighty per cent of the growth will be in the metropolitan and surrounding areas where public water supplies are prevalent. In 1975, municipal water-supply systems in the US served an average 9.5 X 107 mVday (25 bgd) to their customers. About 2.0 X 107 mVday (5.2 bgd), or slightly more than 20 per cent of the total supplied, were delivered to the manufacturing plants. The industry sector obtained, in addition to that from public systems, about 1.4 X 10s mVday (37 bgd) from their own supply sourcesprimarily surface waters. Since manufacturing industries now account for a significant share of the demand for water supplied by municipal systems, and since the growth of the manufacturing sector is projected to be at a much greater rate than that of the population served by the systems, the effects of the different growth rates on municipal water-system development should be appraised. In Fig. 1 are shown projections of Gross Water Demand (the volume of water required if there is no recycling) and Total Water Intake, which is influenced strongly by recycling of treated wastes as substitutes for water intake.