One quick thing you could do. Take a sample of the water to a pool supply
company, they can test for chlorine and stabilizer. If it has stabilizer, it is
pool water. If it is just chlorine it may be city water. They may also know
which minerals would indicate ground water. The extension service can be
helpful there too.
Worst case is it has fecal coliform which would indicate septic/sewer water.
A water test can say a lot about where water was before you got it..