In　this　study,　water　sampling　was　carried　out　extensively　through　collection　of　natural　rainfall　and　municipal　surface　runoff　water　samples　in　the　southeast　region　of　Beijing　Municipality　during　the　period　of　June　2002　to　July　2004.　Chemical　tests　and　measurements　of　collected　water　samples　were　conducted　in　the　laboratory　in　order　to　evaluate　rainwater　quality　and　to　analyze　chemical　stability　of　rainwater.　The　test　results　show　that　the　collected　rainfall　water　and　surface　runoff　water　were　soft　water　and　belonged　to　bicarbonate-calcium　Type-I　water　category.　The　results　also　show　that　their　pH　levels　were　closely　related　to　the　strength　of　alkaline　constituents　in　the　rainwater.　Water　quality　analysis　indicated　that　the　rainwater　collected　from　the　study　region　had　been　contaminated　to　a　certain　degree　by　nitrogen　and　organic　compounds　from　intensive　human　activities.　Water　stability　analysis　focuses　mainly　on　the　potential　of　precipitation-dissolution　of　carbonate　calcium　(CaCO　3　).　The　results　show　that　only　the　rainwater　samples　collected　from　traffic　roads　were　oversaturated　with　respect　to　CaCO　3　and　had　a　tendency　to　precipitate,　while　other　rainwater　samples　were　unsaturated　with　respect　to　CaCO　3　and　had　the　potential　to　keep　dissolving　CaCO　3　into　rainwater.　The　results　obtained　in　this　study　may　help　to　develop　better　rainwater　utilization　strategies　for　alleviating　the　growing　water　shortage　pressure　faced　by　the　City　of　Beijing.