Mo. Rev. Stat. § 67.1748

The metropolitan district shall purchase and use only those materials, products, supplies, provisions and other needed articles produced, manufactured, compounded, made or grown within this state, when such articles are found in marketable quantities in the state and are of a quality suited to the purpose intended and can be secured without additional cost over foreign products or products of other states, provided that quality and fitness of articles shall be considered in purchasing or letting contracts for articles mentioned in this section.