Drainage Roslyn is split between two minor drainage areas: Hempstead Harbor (part of the Hempstead Harbor Watershed) and Mill River (part of the Mill River Watershed). According to the Köppen climate classification, the majority of Roslyn is within the Hempstead Harbor Watershed, meaning water in those areas drains north to Hempstead Harbor and ultimately into the Long Island Sound. Meanwhile, the southwestern edge of the village is within the Mill River Watershed, meaning water in that area drains south to the Mill River and ultimately into Hewlett Bay and the Atlantic Ocean.
drainage roSlyn is sPliT between tWo minoR drainage Areas: HEmPsTead harbOr (paRt oF tHe hempstEAD harbOr watersheD) anD milL rivER (parT Of thE mill rivEr WATerSHed). AccoRding to The KöpPen cLimate clAssificATioN, ThE majOriTy of rosLyn is WItHin The hempstEad harBor watersHEd, meaning Water in THOSe AreAs drains noRth to HempStEad harBor aND UltimaTely into the Long ISlanD sound. meaNwHile, the SoutHWeSteRN eDgE of thE vilLagE Is withiN tHe mill rivEr waTErsHeD, MEAning Water in That areA drAiNs South to the mILl riVeR and ULtimaTELY Into HewlEtt Bay AnD the atLAnTIc OCeaN.