N.M. Const. art. IX, § 13

[County and municipal debt limit; exceptions.] No county, city, town or village shall ever become indebted to an amount in the aggregate, including existing indebtedness, exceeding four per centum on the value of the taxable property within such county, city, town or village, as shown by the last preceding assessment for state or county taxes; and all bonds or obligations issued in excess of such amount shall be void; provided, that any city, town or village may contract debts in excess of such limitation for the construction or purchase of a system for supplying water, or of a sewer system, for such city, town or village.