Dissolved　organic　matter　(DOM)　is　important　in　determining　the　drinking　water　treatment　and　the　supplied　water　quality.　However,　a　comprehensive　DOM　study　for　the　whole　water　supply　system　is　lacking　and　the　potential　effects　of　secondary　water　supply　are　largely　unknown.　This　was　studied　using　dissolved　organic　carbon　(DOC),　absorption　spectroscopy,　and　fluorescence　excitation　-emission　matrices　-parallel　factor　analysis　(EEMPARAFAC).　Four　fluorescent　components　were　identified,　including　humic-like　C1-C2,　tryptophan-like　C3,　and　tyrosine　-like　C4.　In　the　drinking　water　treatment　plants,　the　advanced　treatment　using　ozone　and　biological　activated　carbon　(O3-BAC)　was　more　effective　in　removing　DOC　than　the　conventional　process,　with　the　removals　of　C1　and　C3　improved　by　17.7%-25.1%　and　19.2%-27.0%.　The　absorption　coefficient　and　C1-C4　correlated　significantly　with　DOC　in　water　treatments,　suggesting　that　absorption　and　fluorescence　could　effectively　track　the　changes　in　bulk　DOM.　DOM　generally　remained　stable　in　each　drinking　water　distribution　system,　suggesting　the　importance　of　the　treated　water　quality　in　determining　that　of　the　corresponding　network.　The　optical　indices　changed　notably　between　distribution　networks　of　different　treatment　plants,　which　enabled　the　identification　of　changing　water　sources.　A　comparison　of　DOM　in　the　direct　and　secondary　water　supplies　suggested　limited　impacts　of　secondary　water　supply,　although　the　changes　in　organic　carbon　and　absorption　indices　were　detected　in　some　locations.　These　results　have　implications　for　better　understanding　the　changes　of　DOM　in　the　whole　water　supply　system　to　help　ensure　the　supplied　water　quality.