Dr. Houston in his report for 1913 also stated that 'The striking fact has been shown in my last reports that London is not really drinking merely filtered raw river water but raw river water, which by storage processes has been purified bacteriologically antecedent to filtration to a reasonable extent . . . When it is remembered 90.5 per cent of the samples of raw Thames contain typical B. cob in each cubic centimetre and that 84.8 per cent of the samples of raw Lea water also contains typical B. cob in each cubic centimetre, the transformation which the river water has undergone previous to filtration becomes strikingly apparent.' Dr. Houston strongly advises storage preliminary to filtration and storage he says means sedi mentation, devitalisation and equalization. Nearly the entire supply for London is stored antecedent to filtration. Dr. Houston also stated that per cent of the typhoid bacilli could not be recovered after one week.' Down to 1913 storage and sand filters had efficiently purified the waters used for potable purposes in London. Dr. Houston, however, in his report for the year recommended sup plementary processes of purification. Since 1917 the entire water supply of London has been treated with chlorine. Before filtration, it re ceives a dose of calcium hypochlorite. Slow sand filters are now used at the various works.
The twelfth annual report of Director Hous ton for the year 1917-18, contains an exhaustive report of chlorination, super-chlorination and de-chlorination experiments with 224 micro photographs.
The thirteenth annual report of the director for the year ending 31 March 1919, discusses the scientific results of the chlorination of the Thames and New River raw river waters and chlorination in relation to filtration and the condition of the raw and filtered waters. On 31 March 1919, the equipment of the London water supply under the Metropolitan Water Board comprised 48 storage reservoirs with a total capacity of 1,981,500.000 gallons and 86 service reservoirs for filtered water with a capacity of 310,900,000 gallons and its 172 filter beds had a total area of 170.7 acres.
Liverpool obtains its supply from wells, from eight impounding reservoirs in the water shed, Ravington having a capacity of 4.1 billion gallons and from the impounding reservoir, the largest in Europe, 82S feet above sea-level, formed by a dam 1,172 feet long and 84 feet high across the valley of the Vyrnwy River, formerly a glacial lake in north Wales, having a capacity of 12 1/7 billion gallons. The im pounded waters from the Ravington reservoirs are delivered through a 44-inch cast-iron pipe 24V miles long to Liverpool and from Vyrnwy reservoir through a 39-inch cast-iron pipe 63 miles long and a tunnel 4 miles long to Pres cott reservoir at Liverpool. The water is filtered through sand filters and otherwise treated. Upward of 38.000.000 gallons are con. sumed daily in Liverpool which is at the rate of 40 gallons per capita per day. An additional reservoir has been constructed near Malpas and a high-level tank has been built at Woolton Hill.
Manchester obtains its water supply from the elevated Longdcndalc watershed with seven Of more impounding reservoirs along the Etherow River and from Lake Thirlmere miles long and 533 above sea-level in the north western part of England. The outlet of the lake is closed by a masonry structure 857 feet long and 104% feet high from the low est part of the gorge outlet. That enlarges the lake to three and one-fourth miles in length and gives it a capacity of eight and one-seventh billion gallons. The aqueduct leading to the city is 95 miles long and carries 50,000.000 gallons per day. The storage reservoirs of Manchester have a capacity of upward of 41.000,000 gallons. Its daily consumption is 40 gallons per capita and aggregates 50,000,000 gallons. A third con duit has recently been constructed from the lake to the city.
Birmingham, England, formerly obtained its water supply from five local streams and eight wells. From these the water was pumped into six service reservoirs at different elevations and into a stand-pipe. All such waters were filtered. In 1900 there were 12 sand filter beds with a total area of eight and one-fourth acres. In 1892 Parliament authorized Birmingham to draw an additional supply from Elan and Claerwen rivers in Wales. It constructed six long reser voirs by building masonry dams across the narrow valleys of those rivers, one of which dams was 600 feet long and some were more than 100 feet in height above the bed of the gorges so closed. They had a combined ca pacity of 18,000,000,000 gallons. There were also constructed 30 filter beds for the filtration of all such waters. This improvement contem plated a supply of 75,000,000 gallons a day for service in addition to 27,000.000 gallons to com pensate for losses to riparian operators along the Wye.
The water flows by gravity through the Elan aqueduct 73.3 miles to Birmingham From the elevated sources to the high service reservoirs in Birmingham there is a fall of 170 feet.
In 1913 there were consumed 27,471.991 gallons daily, which was an average of 3224 gallons for each resident Glasgow obtains its water supply from Brock Burn six miles from the city through its Gorbals works into four impounding reservoirs, having a combined capacity of 1.000,000,000 gallons or more and also from Loch Katrine 364 feet above sea-level, having a storage capacity of five and two-thirds billion gallons. The water was conducted by gravity through aqueducts and tunnels 27 miles to Mugdock and Craig maddie reservoirs, having a combined capacity of one and one-fifth billion gallons. Reservoirs have been constructed in the valley of the Teich to compensate for waters drawn by the city. In 1895 it was decided to connect by the tunnel Loch Arklet 455 feet above sea-level with Loch Katrine and raise the outlet of the latter five feet and thereby secure a storage capacity of 205 billion gallons in the two lochs. An ad ditional reservoir with a capacity of 694,000. f100 gallons has been constructed. In 1913-14 Glasgow daily consumed 75 gallons per capita Or an aggregate of F+5,000.000 gallons.