Shipboard bilges can be a sink and reservoir for a range of substances other than oil and water, i.e., particles, chemicals, biological activity, any of which alone or in combination can cause an oily water separator (OWS) and related bilge water treatments systems to fail. Borrowing from the data processing / computer industry,"garbage in, garbage out." To assist the operator in properly identifying contaminants and troubleshooting occurring OWS systems failure we developed a daignostics kit to complement the internationally recognized "Guide to Diagnosing Contaminants in Oily Bilge water to Maintain, Operate and Troubleshoot Bilge water Treatment Systems." The Guide and our Bilge Water Dianostics Kit assists shipboard engineers to troubleshoot OWS and prevent and remedy most OWS system failures.