Section 198.18 - District bonds(1) ISSUE, GENERAL LIABILITY. Bonds of the district may be issued to raise funds with which to purchase any permanent property for the district, to refund any valid, subsisting bonded debt of the district and for the purpose of paying and discharging any plant mortgage certificates or purchasing and retiring any bonds, notes or other evidences of indebtedness secured by any mortgage or deed of trust upon property acquired by the district, subject to the limitation of total indebtedness of the district contained in s. 198.14 (9). Except as otherwise provided by this chapter all bonds of the district shall be and constitute a general liability of the district and the holders thereof shall have the benefit of all legal remedies to compel the payment of the interest thereon as the same shall fall due and the principal thereof at maturity, and, in the event of any default in the payment of interest or principal when due, to compel the levy and collection of taxes by the district on all property subject to taxation therein to pay the same.(2) TAXABILITY. The bonds, plant mortgage certificates, notes or other evidence of indebtedness which may be issued, made or negotiated by the district and the income thereof shall be subject to taxation upon the same basis as the obligations of private utilities.(3) LIMITATION OF ACTION. Bonds of the district shall be incontestable, except upon constitutional grounds, after the time provided by s. 893.77 (3), and the substance of this provision and s. 893.77 (3) shall be stated upon the face of each bond.(4) INVESTMENTS BY DISTRICTS. Reserve funds carried by the district may be invested in any bonds or plant mortgage certificates issued by the district, provided that before purchasing any of its own issues the district shall advertise for offers and purchase first those issues which, interest accrued and maturities considered, are offered at the best net price to the district. Reserve funds of the district may also be invested in the bonds or plant mortgage certificates of any other district and in any of the kinds of securities or forms of investments enumerated in s. 201.25, 1969 stats.(5) TRUST FUND INVESTMENTS. Bonds and plant mortgage certificates issued by any district shall be lawful investments for any trust funds held by the state or any state institution, for any reserve or debt service funds of any municipality, for the assets of any bank, trust company, or of any trust estate and shall be accepted as deposits for any purpose for which deposit of securities may be required or authorized by law.1971 c. 260 s. 92 (3); 1979 c. 279, 323; 1981 c. 390 s. 252; 1983 a. 207 s. 93 (8).