Well my little town used to tout itself as the best water on Earth. We got an urgent bulletin that our water is now tainted. I guess the spring source has been found to contain E coli. We now have to boil our water to drink it. I don't know wtf they do to fix it if the spring itself is contaminated. I must admit this is kind of scary. I just hope we don't end up with a bunch of sick people.
They most likely will chlorinate it or eventually install a system that kills the bacteria by exposure to UV light. There are several chemicals close to Chlorine, that do the job economically also.
There isn't much that is alive that chlorine will not kill even in a small dose including you. They will dose the spring and system initially then if the problem persists they will inject chlorine/etc into the water system continuously.
Your town will end up with a water treatment plant of some sort as small as it maybe. Once you have an event like this often the government demands it, even if the water gets clean again.
Switching to bottled or purified water if you can afford to is the best thing till they get the bacteria under control and get the water treatment figured out. They will be sending some higher doses of chemicals through the system trying to sterilize it at first. Then they will be fooling around trying to get the amount of chemistry correct . During those periods especially, it would be preferable not to be drinking the water.
Right now they are scrambling to find the source of the contamination. When you have a lot of run off in the spring these things are more prone to happen. Large animals die and are not found and buried correctly, waste treatment system over flow, soil that acted as filters to the aquafir slides away, that sort of stuff. At least they caught it before people began getting sick.