The Commissioner, upon receipt of information that a contaminant which is present in or is likely to enter a public water system may present an imminent and substantial endangerment to the health of persons, may take such actions as he may deem necessary in order to protect the health of such persons. The actions which the Commissioner may take include (but shall not be limited to) (a) issuing such orders as may be necessary to protect the health of persons who are or may be users of such system (including travelers), and (b) commencing a civil action for appropriate relief, including a restraining order or permanent or temporary injunction.