In 1984, members of the Rajneeshee religious cult contaminated a city water supply tank in The Dalles, Oregon, using Salmonella and infected 750 people.
[1] In 1992 The Kurdistan Workers' Party (PKK) put lethal concentrations of potassium cyanide in the water tanks of a Turkish Air Force compound in Istanbul.
[1] In 2000, Queensland police arrested a man for using a computer and a radio transmitter to take control of the Maroochy Shire wastewater system and release sewage into parks, rivers and property.
Despite the fact that it is impractical and very unlikely to produce any effect at large scale, during the 1960s a great deal of attention was paid to the notion that counter-culture figures could intoxicate a whole city by putting a small dose of LSD in the water supply.
[2] In November 1966 Vue magazine ran "Why They Had to Outlaw LSD", in which writer WH Carr claimed that "[A] few ounces of it, dumped in the water supply of a major city, could shake up millions.