Archaic word for waterfall; modern Japanese uses 滝 (たき). Found in classical literature and place names.
See also: 滝
In classical texts, 垂水 is read as たるみ and can refer to a waterfall.
張り is tautness or firmness, while たるみ is the sagging or slackness that results when that tautness is lost.
From 垂る水, “falling water,” with 垂る the classical attributive form of 垂る, “to hang or fall.” The expression contracted to たるみ.