ABSTRACT
Men have lived in towns for thousands of years, but the great city of today is a very modem phenomenon. The vast aggregations of population, numbering millions, to be found in the largest towns could not have been supplied with enough food to keep them alive for a single day before the advent of modem means of transport. The railway, the motor car, the cargo ship driven by steam or oil, are the veritable founders and supporters of the great modem city. We are equally dependent on modem technology for the conveyance, filtration and distribution of the enormous quantities of water required by the citizens of every large city for domestic, industrial and commercial uses. The Pont du Gard in Provence is a superb relic of a Roman aqueduct which successfully carried water a considerable distance; but the Romans would have been totally unable to provide London or Paris with the quantities of water they consume today.
