The water knot is a knot

Knot

A knot is a method of fastening or securing linear material such as rope by tying or interweaving. It may consist of a length of one or several segments of rope, string, webbing, twine, strap, or even chain interwoven such that the line can bind to itself or to some other object—the "load"...

 frequently used in climbing

Climbing

Climbing is the activity of using one's hands and feet to ascend a steep object. It is done both for recreation and professionally, as part of activities such as maintenance of a structure, or military operations.Climbing activities include:* Bouldering: Ascending boulders or small...

 for joining two ends of webbing

Webbing

Webbing is a strong fabric woven as a flat strip or tube of varying width and fibres often used in place of rope. The name webbing comes from the meshed material frequently used in its construction, which resembles a web...

 together, for instance when making a sling

Sling (climbing equipment)

A sling or runner is an item of climbing equipment consisting of a tied or sewn loop of webbing that can be wrapped around sections of rock, hitched to other pieces of equipment or tied directly to a tensioned line using a prusik knot; for anchor extension , equalization, or climbing the...

.

Tying the water knot

It is tied by forming an overhand knot

Overhand knot

The overhand knot is one of the most fundamental knots and forms the basis of many others including the simple noose, overhand loop, angler's loop, reef knot, fisherman's knot and water knot. The overhand knot is very secure, to the point of jamming badly. It should be used if the knot is...

 in one end and then following it with the other end, feeding in the opposite direction.

The ends should be left at least 3 inches (7.6 cm) long and the knot should be "set" by tightening it with full body weight. The ends can be taped or lightly sewn

Sewing

Sewing is the craft of fastening or attaching objects using stitches made with a needle and thread. Sewing is one of the oldest of the textile arts, arising in the Paleolithic era...

to the standing parts to help prevent them from creeping back into the knot.

Security

Testing has shown the water knot to slip very slightly, but very consistently, with each load and unload cycle. In tests using 9/16 in (14.3 mm) tubular webbing, repeated loading and unloading with 250 lbs (113 kg) caused one of the 3 in (76 mm) tails to work back into the knot in just over 800 loading cycles. When the water knot was statically loaded with 200 lbs (91 kg) no slipping was observed. These results validate the need to leave long tails and inspect water knots before each use.