Before Baltimore started on its quest for pure and wholesome drinking water, we need to look at a brief history of water treatment itself. This, I believe, was best documented in Joseph Ellms 1917 book Water Purification. He starts off  by describing the Ancient Systems of Water Supply as such:

            Among primitive peoples the question of water supply was never of pressing importance, except in arid and semi-arid regions…springs were sought for, wells were dug, and cisterns constructed in order that a supply of water might at all times be available. Wells of great antiquity may be found in Egypt (Joseph’s well was 297 feet deep in solid rock) and India. The Chinese were familiar with the driving of artesian wells. Domestic filters of unglazed earthenware or of sandstone were known to have been used by ancient Egyptians and by the Japanese…siphoning water from one vessel to another through porous material was well known to the ancients. As populations became more dense…the need for larger volumes of water…became urgent. The ancient water tanks of Aden, in Arabia, collected surface waters from the gorges of a volcanic crater…example of an impounding reservoir…may have been built by the Persians as early as 600 B.C. Probably no more elaborate system of public water supply was provided for any ancient city than that of Rome…water conveyed by aqueducts. These were built between 321 B.C. and 305 A.D. At the time of the fall of Rome…many were destroyed or fell to disease. The Moors in Spain during the ninth century constructed some important works, also rebuilding the older Roman works. London was first supplied in small quantities with spring water conducted through lead pipes and masonry conduits. In 1582 a pump was erected on London Bridge to take water from the River Thames and to deliver it through the lead pipes. The growth and development of water works plants in reality dates from the eighteenth century…not until the latter half of the nineteenth century was very rapid progress made.

Mr Ellms then notes four epochs concerning water purification within the United States: First was James P. Kirkwood’s report on the “Filtration of River Waters” in 1866. Second was the work of the Massachusetts’s State Board of Health in 1887. Third was experimentation on turbid waters starting with Louisville, Kentucky in 1896 and the fourth being from 1908 when the disinfection of the water, on an experimental basis, with hypochlorite of lime, started in Chicago. This method became widespread over the next five years. Meanwhile, experimentation in both Europe and the US continued; using chlorine, ozone and ultra-violet light.