If the Sellers knew about this, and didn't DISCLOSE it to you, they are liable.
The only exception to this is if it is a Foreclosure, then, because the Bank did not OCCUPY the house, they would not have to give you DISCLOSURES.
On the other side of the coin, the phrase "Caviat Emptor" applies, Buyer Beware: You have the chance to protect yourself with an Inspection Contingency: If you didn't do that, and in particular, if you did not choose to inspect the well, then you are buying it as-is and you don't have recourse.
This information is in general, and may be different according to local and state laws.
Good luck and may God bless