It provides a way for the house service pipe to penetrate the side of the well casing with a supposedly contaminationproof seal. The hole in the casing has to be made with a hole saw for the best results. If it is made with a cutting torch, then the hole may be offsize or the edges ragged preventing a proper seal, and once it is buried, (the pitless part of the label), the deficiency would not be detectable. The latter would be a good reason for Wisconsin not allowing them.: In an underground well, what is the purpose of a pitless adapter? Why do some localities not approve of them? What would you use in place of one?