Due　to　their　recent　widespread　use,　nanoparticles　(NPs)　may　contaminate　water　sources　and　pose　a　health　risk.　Thus,　it　is　important　to　understand　the　fate　of　NPs　in　order　to　evaluate　potential　threats.　Here　we　show　that　the　presence　of　anions　influences　the　stability　of　NPs　in　synthetic　and　lake　water.　Concentrations　of　0.3　and　3　mM　PO43-　exhibited　stronger　stabilizing　effects　on　NPs　than　30　mM.　Moreover,　chloride　ions　promoted　the　coagulation　of　TiO2　NPs　over　a　range　of　concentrations　(0.3-30　mM　elicited　similar　effects).　On　the　other　hand,　phosphate　was　found　to　hinder　the　coagulation　effect.　These　results　are　expected　to　contribute　to　novel　water　purification　strategies　for　the　efficient　removal　of　NPs.　Further　experiments　should　focus　on　the　mechanism　of　phosphate　on　the　removal　of　NPs　in　the　coagulation/flocculation/sedimentation　(C/F/S)　process.