Wtr rsrcs r ntrl rsrcs f wtr tht r ptntlly sfl fr hmns, fr xmpl s src f drnkng wtr spply r rrgtn wtr. Ths rsrcs cn b thr frshwtr frm ntrl srcs, r wtr prdcd rtfclly frm thr srcs, sch s frm rclmd wtr (wstwtr) r dslntd wtr (swtr). 97% f th wtr n rth s slt wtr nd nly thr prcnt s frsh wtr; slghtly vr tw-thrds f ths s frzn n glcrs nd plr c cps. Th rmnng nfrzn frshwtr s fnd mnly s grndwtr, wth nly smll frctn prsnt bv grnd r n th r. Ntrl srcs f frsh wtr ncld srfc wtr, ndr rvr flw, grndwtr nd frzn wtr. Ppl s wtr rsrcs fr grcltrl, ndstrl nd hshld ctvts.
Wtr rsrcs r ndr thrt frm mltpl sss. Thr s wtr scrcty, wtr plltn, wtr cnflct nd clmt chng. Frsh wtr s n prncpl rnwbl rsrc. Hwvr, th wrld's spply f grndwtr s stdly dcrsng. Grndwtr dpltn (r vrdrftng) s ccrrng fr xmpl n s, Sth mrc nd Nrth mrc.