Wells used for 'city water' are much larger diameter and very deep; like over a thousand feet plus in many cases. Their recovery rate is usually in the high hundreds of gallons per minute. When the recovery rate falls, the pump quits, etc, etc, the well is usually shut down for the repair or for rehabilitation or shut down permanently or used sparingly.
It is not that the well's water changes hardness, although sometimes it does because of drought or rainy periods or new wells being drilled or blasting etc..
Most cities have many wells, Rochester MN had 36 wells about 12 years ago and a few surface water sources. A city mixes/blends various waters to get the hardness, pH etc. they want or need to meet certain regs. When a well goes down they can have an increase of hardness in their system, that's why they state the range of hardness in their annual report from the low to high in their system.
And that is why softners on 'city' water should be sized and programmed for the highest water in the city system; instead of using a test result of the water.
I doubt a city water company would know much about private residential well water quality simply because they have no need for the info and residential type wells are rarely into any deep aquifer such as their wells are.