Constitution of the State of Ohio Art. XVIII, § 6

Any municipality, owning or operating a public utility for the purpose of supplying the service or product thereof to the municipality or its inhabitants, may also sell and deliver to others any transportation service of such utility and the surplus product of any other utility in an amount not exceeding in either case fifty per cent of the total service or product supplied by such utility within the municipality, provided that such fifty per cent limitation shall not apply to the sale of water or sewage services.