The ruins of antiquity show that large storage reservoirs were common in ancient times, and it is well known that the Chinese for thousands of years have used alum as a coagulant in muddy water in order to accelerate clarification. Perhaps the earliest literary reference to filtration appears in the "Ousruta Sanghita," a collection of medical lore written in Sanskrit probably 4,000 years ago. In a letter to the British Journal of Preventive Medicine, Mr. Francis E. Place, of Jaipur, Rajputana, India, calls attention to this reference, in which the following statement appears: "It is good to keep water in copper vessels, to expose it to sunlight, and to filter it through charcoal."

Fig. 2. Water-cooler.

1 Geological Survey, Water-Supply Paper 315.

Modern history does not record any attempt at filtration until 1829, when the 1-acre slow sand filter was built by James Simpson for the East Chelsea Water Co., at London, England. The germ theory of disease was then unknown, and the filter was built to perform the offices of a mechanical strainer for the purpose of removing the turbidity from the water. This filter is still in service, however, and is doing work of a nature far exceeding the purpose for which it was designed and built.

Typhoid fever as a specific disease was discovered in 1829, but it was not until 1849 that the germ theory of disease was seriously advanced. An act of the British Parliament of 1852 made compulsory the filtration of the entire water supply of the metropolitan district. This action was the result of the severe cholera epidemic of 1849 and was the first of a series of attempts to purify water for hygienic reasons.

The first noteworthy movement in this country for the purification of a public water supply was made in 1866, when the city of St. Louis sent James P. Kirkwood to Europe with instructions to investigate the art of the purification of water as there practised. On his return Mr. Kirkwood made an elaborate report, which will always remain one of the classics on the subject. His recommendations for St. Louis were not adopted, however, apparently for sound reasons, as none of the purification works in Europe which came under Mr. Kirkwood's observation had a water to treat that was similar to the water at St. Louis. The waters of western Europe are almost uniformly clear, whereas that of the Mississippi is extremely turbid.

In 1872, about five years before Mr. Kirkwood's death, a plant was built at Poughkeepsie, N. Y., in accordance with his plans. This was the first practical attempt at purification of a municipal water supply in America. Plants of a type similar to that built at Poughkeepsie were built somewhat later at Lowell, Mass., Columbus and Toledo, Ohio, and elsewhere, but most of them failed of the purpose for which they were intended.

Quite extensive experiments on slow sand filtration were also made at Boston, Mass., Louisville, Ky., and elsewhere.

The classic investigations of the Massachusetts State Board of Health at Lawrence, Mass., were begun in 1887 and are still in progress. Up to a few years ago the work at the Lawrence Experiment Station, so far as water purification is concerned, was limited to studies on slow sand nitration. The construction of the Lawrence city filter, first placed in operation in 1893, was one of the results of these investigations.

In 1893 the first carefully conducted experiments with the newer process of mechanical water purification were made by Edmund B. Weston on the water supply of Providence, R. I., and in 1895 the much more elaborate studies in the same line were begun at Louisville, Ky., and continued through 1897. These Louisville experiments, conducted under the direction of George W. Fuller, formed the beginning of practical demonstrative investigations into the various methods of water purification. Similar studies followed successively at Pittsburgh, Pa.; Cincinnati, Ohio; Washington, D. C; New Orleans, La.; Philadelphia, Pa.; and elsewhere.

All of this experimental work gave a great impetus to water purification in this country, and not only has the number of cities installing water-purification works increased rapidly during the last 10 years but the design and construction of such works has now reached a high plane of excellence. The more advanced ideas in this regard were first manifested in the works at Albany; N. Y., designed by Allen Hazen, and in the works of the East Jersey Water Co., designed by George W. Fuller and built at Little Falls, N. J. The former plant was first used in 1899 and the latter in 1902. At Albany the filters are of the slow sand type, and at Little Falls of the mechanical or rapid sand type.

In 1900, according to Hazen, 1,860,000 people, or 6.3 percent of the urban population of the United States were being supplied with filtered water. In 1904 the number of people so supplied had increased to 3,160,000, or 9.7 percent of the urban population of the country. Since that time many large cities have installed filter plants until now (1918) about 15,000,000 people in the United States are being served with filtered water.