Outbreak of cholera drove development of reservoir
The brainchild of Sir John Gray (1816-1875), development of the Vartry reservoir was in part driven by Dublin's cholera epidemic of 1832 where more than 5,200 people died.
In October 1860, a Royal Commission recommended that a new supply be urgently delivered from the Vartry River in Wicklow at a cost of around £500,000, the equivalent of around €71m today.
But the proposal was fiercely resisted by the canal companies, which supplied the city with water and faced financial ruin.
A paper from Dublin City Council's Michael Corcoran to Engineers Ireland noted that the companies indulged in "many underhand ploys" to delay the scheme.
A nationalist politician, Gray pushed the 1861 Dublin Corporation Waterworks Act through the Houses of Parliament, which allowed the scheme to go ahead. He also bought up all the necessary land and transferred it to the Corporation at cost, to avoid speculators profiting.
He was knighted for his work on Vartry, and his statue looks down on O'Connell Street.
Work began in November 1862 and took six years to complete. An embankment was constructed to create a reservoir, with sufficient capacity for 200 days' supply. Seven filter beds were included, with three more added in 1873. Another four were built in 1930, and two more in 2005.
Work on the Callow Hill tunnel began in 1863, and was completed in September 1866. Reservoirs were also built in Stillorgan, where the treated water was stored.
The supply only failed once, in the drought of 1893.