(2) No county, city, town, village, school district, sewerage district or other municipal corporation may become indebted in an amount that exceeds an allowable percentage of the taxable property located therein equalized for state purposes as provided by the legislature. In all cases the allowable percentage shall be 5 percent except as specified in pars. (a) and (b):
(b) For any school district which offers no less than grades one to 12 and which at the time of incurring such debt is eligible for the highest level of school aids, 10 percent shall be permitted.
(4) When indebtedness under sub. (2) is incurred in the acquisition of lands by cities, or by counties or sewerage districts having a population of 150,000 or over, for public, municipal purposes, or for the permanent improvement thereof, or to purchase, acquire, construct, extend, add to or improve a sewage collection or treatment system which services all or a part of such city or county, the city, county or sewerage district incurring the indebtedness shall, before or at the time of so doing, provide for the collection of a direct annual tax sufficient to pay the interest on such debt as it falls due, and also to pay and discharge the principal thereof within a period not exceeding 50 years from the time of contracting the same.
(5) An indebtedness created for the purpose of purchasing, acquiring, leasing, constructing, extending, adding to, improving, conducting, controlling, operating or managing a public utility of a town, village, city or special district, and secured solely by the property or income of such public utility, and whereby no municipal liability is created, shall not be considered an indebtedness of such town, village, city or special district, and shall not be included in arriving at the debt limitation under sub. (2).
