When the director of environmental protection finds, upon investigation, that water in a public water system is subject to the danger of contamination by reason of unsatisfactory location, protection, construction, operation, or maintenance of the system, or by reason of the existence of an unsafe emergency system or connection to an unsafe private or auxiliary system, or if the director finds upon investigation that the public health is endangered by reason of the existence of an inadequate public water system, or that the system does not contain quantities of fluoride as required by section 6109.20 of the Revised Code, he shall notify the municipal corporation, county, public institution, or person, owning or operating such public water system of his findings and of the time and place, when and where a hearing may be had. Such notice shall be by personal service, or shall be sent by certified mail to the mayor or managing officer or officers of the municipal corporation, county, or public institution or to the person owning or operating such supply.