I am unfamiliar with a "perpetual contract" and that phase does not appear in any reported appellate court decision of the State of Oklahoma. However, usually unpaid utility bills do constitute a lien against the property that is enforceable against a subsequent purchaser, which has the same practical effect. This kind of obligation is also sometimes described as an "encumbrance".
Usually, in an arms length sale of real estate through real estate agents, a title insurance company is hired and is responsible for determining if there are any outstanding liens, pro-rating utility bills, pro-rating property taxes, etc. at closing. If the title company fails to find a lien and there is one, the title company is responsible for paying off the lien that it failed to find (although it can often force the previous owner to indemnify it for the payment it has to make).
It could be that since water service was not currently being delivered, that the title company did not search in the manner that it should have to find this lien, or it could be that there was no title company used and so no one ever checked.
Also, if the property was conveyed with a "warranty deed" such a deed contains a promise from the seller that there are no liens or encumbrances not listed on the face of the deed that have to be paid, and the seller has liability for breach of the warranty of title. But, if the property was conveyed with a "quitclaim deed" there is no such warranty.