Districts for four years (1974–77) before taking a position as a chemist with the Metropolitan Water District of Southern California in 1977. From the beginning of his career at Metropolitan, Krasner worked at the water quality laboratory which is located at the F.E. Weymouth Treatment Plant in La Verne, California. He held increasingly responsible positions as Research Chemist, Senior Chemist and Senior Research Chemist until being promoted to Principal Environmental Specialist in 1997. He retired from Metropolitan in September 2018. As Principal Environmental Specialist, Krasner was responsible for the technical direction of DBP research at Metropolitan, as well as studies on the control of other micropollutants of health, regulatory, and aesthetic significance. He was involved in the design of experimental plans for natural organic matter (NOM), DBP, and PPCP research studies, project management, and interpretation of findings. In 1989, his article on the first national survey of multiple-DBP occurrence has received over 1,000 citations by other authors. Another survey of a new generation of DBPs in 2006 has been cited over 1,100 times. A few of the many externally funded projects for which he was responsible include: Co-Principal Investigator of a National Science Foundation (NSF) project on “Drinking Water Safety and Sustainability: Identifying Key Chemical Drivers of Toxicity for Long-Term Solutions in the United States.” (2017 – present) Technical advisor for a project on “Global Assessment of Exposure to Trihalomethanes in Drinking Water and Burden of Disease” being conducted by the Barcelona Institute for Global Health (ISGlobal). (2017 – present). Principal investigator for Water Research Foundation project on “Nitrosamine Occurrence Survey.” (2013 – 2016).” Co-principal investigator for Water Research Foundation project on “Investigating Coagulant Aid Alternatives to polyDADMAC Polymers.” (2012 – 2015) Principal investigator for Water Research Foundation project on “Controlling the Formation of Nitrosamines during Water Treatment.” (2012 – 2015) Co-principal investigator for Water Research Foundation project on “Optimizing Conventional Treatment for Removal of Cyanobacteria and their Metabolites.” (2011 – 2015) He was a consultant to the drinking water community since 1983. Some of his projects included: Peer reviewer for Imperial College, London, of report on “Review of the Current Toxicological and Occurrence Information Available on Nitrogen-Containing Disinfection By-Products.” Technical advisor to the University of the Aegean on reinterpreting DBP data for a European Union project (HiWATE) on DBPs. Technical auditor for the European Commission on laboratory practices for a project (HiWATE) on DBPs. Technical advisor for Scottish Executive