The change in water quality in Flint, Michigan, was primarily caused by the decision to switch the city's water supply from Lake Huron (through the Detroit water system) to the Flint River in order to save money. This switch involved the city not treating the water properly, which led to corrosion of the pipes and leaching of lead into the drinking water.
Thus, the most accurate response would be:
The city was taken off the Detroit water system to save money.