Where phrase jerk water town originate

Jerkwater - a train on an early branch railroad

Etymology: jerk + water: prob. in reference to pulling the valve on the water tank to fill the engine boiler

(adjective) Informal small, unimportant, etc.

http://www.yourdictionary.com/jerkwater

1. small and unimportant: remote from population centers and considered insignificant and backward

2. lacking significance: lacking consequence or significance

[< supplying water to early trains in remote places with a bucket on a rope]

http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861623064

1 : remote and unimportant <jerkwater towns>
2 : trivial

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=jerkwater

—adj.
1. Informal.insignificant and out-of-the-way: a jerkwater town.
2. (formerly) off the main line: a jerkwater train.

—n.
(formerly) a train not running on the main line.

http://www.infoplease.com/dictionary/jerkwater

It's jerkwater town = Remote, small, and insignificant: a jerkwater town.

From jerkwater, a branch-line train, so called because its small boiler had to be refilled often, requiring train crews to “jerk” or draw water from streams.

In the old days when there was no indoor plumbing people had pumps outside their homes. They would prime the pump with a little water and they pumped the handle steadily until fresh water would come. This process was referred to jerking the pump and the motion was called jerking. Later on people got indoor plumbing but in the small towns where people were too poor or just too stupid to get the indoor plumbing were often referred to as jerks because they were still jerking the pumps. Thus dumb people were called jerks to indicate lack of common sense or just plain stupid (but poverty did not play a major part, although poverty often played a role on stupid people).