53 Pa. Stat. § 7251
In addition to the remedies provided by law for the filing of liens for the collection of municipal claims, including but not limited to water rates, sewer rates and the removal of nuisances, all cities, boroughs, incorporated towns, townships and bodies corporate and politic created as municipal authorities pursuant to law may proceed for the recovery and collection of all of the foregoing claims by action of assumpsit against the person or persons who were the owner or owners of the property at the time of the completion of the improvement, or at the time the water or sewer rates or the cost of the removal of nuisances first became payable notwithstanding the fact that there was a failure on the part of any such city, borough, township, or body politic and corporate created as a municipal authority pursuant to law, or its agents, to enter any such municipal claim as a lien against the property assessed for the improvement, or for the furnishing of water or sewer services and for the removal of nuisances and for the recovery of which the action of assumpsit was brought. Any such action in assumpsit shall be commenced either within six years after the completion of the improvement from which said claim arises or within six years after the water or sewer rates or the cost of abating a nuisance first became payable.
53 P.S. § 7251