The　overall　goal　of　urban　water　supply　is　to　ensure　the　water　quality　from　source　to　tap.　As　the　＂last　mile＂,　the　building　water　supply　system　(BWSS)　is　the　crucial　part　in　ensuring　tap　water　safety,　and　its　deteriorating　water　quality　has　attracted　increasing　attention.　In　this　work,　we　provide　a　comprehensive　overview　of　the　pollution,　configuration,　purification　and　regulation　of　BWSSs,　with　a　focus　on　ensuring　water　quality　safety.　Periodic　water　usage　in　buildings　is　a　unique　feature　that　leads　to　intermittent　water　stagnation　and　reduced　residual　chlorine.　Biological　pollution　has　become　a　key　focus　of　existing　studies　due　to　its　acute　effects　on　human　health,　compared　to　the　chronic　effects　of　chemical　pollution.　For　new　systems,　water　quality　risks　can　be　reduced　at　the　source　by　optimizing　pipe　materials　and　reasonable　layout.　It　is　recommended　to　introduce　secondary　disinfection　technologies,　as　they　are　important　for　ensuring　biosecurity.　Moreover,　supervision　and　maintenance　are　the　basis　for　long-term　efficient　operation　of　BWSSs.　This　review　constructs　a　framework　for　controlling　water　quality　deterioration　based　on　the　wholse　process,　which　is　instructive　for　the　design,　operation,　maintenance　and　management　of　BWSSs,　and　provides　relatively　clear　research　directions　for　improving　water　quality.