Where did it start?

 Concerning the 'practice' of putting sodium fluoride into drinking water, where did it begin?

Historically, in the 50's and 60's, Sodium Fluoride was quite expensive to dispose of.

From personal research, the very first occurrence of purposefully putting sodium fluoride into drinking water was in the German ghettos and in Nazi Germany's infamous prison camps.

The Gestapo you see had little concern about sodium fluoride's 'supposed' effect on children's teeth; instead, their reason for mass-medicating water with sodium fluoride was to sterilize humans and force the people in their concentration camps into calm, bovine, submission.

(See for reference: "The Crime and Punishment of I.G.Farben" written by Joseph Borkin.)

Sodium Fluoride is also one of the basic ingredients in both PROZAC (FLUoxetene Hydrochloride) and Sarin Nerve Gas (Isopropyl-Methyl-Phosphoryl Fluoride). The same Sarin Nerve Gas that was used on a crowded Japanese subway train.
Source: http://www.infowars.com/pdfs/tapwater.pdf
Source: http://www.japan-101.com/culture/sarin_gas_attack_on_the_tokyo_su.htm

Dr. E.H. Bronner, Mfg. Research Chemist, Los Angeles:

The practice began in the U.S. in 1945 and was endorsed by the U.S. Public Health Service (PHS) in 1950.

Very few countries have adopted this practice to any significant extent. Only eight countries in the world have more than 50% of their populations drinking artificially fluoridated water (Australia, Colombia, Ireland, Israel, Malaysia, New Zealand, Singapore, and the U.S.).

In Europe, only Ireland (with 73% of the population fluoridated), the U.K. (10%) and Spain (10%) fluoridate some of their water supplies. In the U.S., about 70% of the population is drinking fluoridated water – that is approximately 200 million people and about half the number of people drinking artificially fluoridated water worldwide.

Some countries have areas with high natural fluoride levels in the water. These include India, China and parts of Africa. In these countries measures are being taken to remove the fluoride because of the health problems that fluoride can cause.

Fluoride is the only chemical added to water for the purpose of medical treatment. The U.S. Food and Drug Administration (FDA) classify fluoride as a drug when used to prevent or mitigate disease (FDA 2000).

As a matter of basic logic, adding fluoride to water for the sole purpose of preventing tooth decay

(a non-waterborne disease) is a form of medical treatment. All other water treatment chemicals are added to improve the water's quality or safety, which fluoride does not do.

Healthy adult kidneys excrete 50 to 60% of the fluoride they ingest each day (Marier & Rose 1971). The remainder accumulates in the body, largely in calcifying tissues such as the bones and pineal gland (Luke 1997, 2001). Infants and children excrete less fluoride from their kidneys and take up to 80% of ingested fluoride into their bones (Ekstrand 1994). The fluoride concentration in bone steadily increases over a lifetime (NRC 2006).

Since swallowing fluoride is unnecessary, and potentially dangerous, there is no justification for forcing people (against their will) to ingest fluoride through their water supply.

Reference: http://www.rense.com/general79/hd3.htm