Maji na yale yale tu hayaongezeki, yanachofanya ni kuhama tu kutoka reservoir moja kwenda nyingine (water cycle) Baadhi ya reservoirs ni bahari, maziwa, mito, anga,mimea, underground, wanyama, na barafu hasa zilizoko Actic na Antarctic. Tuyatunze maji haya yaliyopo hayaongezeki.