The water knot — also called the "tape knot," "ring bend," or "overhand follow-through" — is the standard climbing knot for joining two ends of flat webbing into a closed loop. It is essentially a follow-through overhand knot: an overhand knot tied in one end of the webbing, then the other end threaded back through the knot tracing the same path. The result is a clean, low-profile join that holds well in tubular nylon webbing.
Climbers use the water knot to make slings, runners, and anchor material from bulk webbing — tubular nylon or Dyneema. Pre-sewn slings have largely replaced field-tied water knot slings in modern climbing because sewing is stronger and more consistent than knots. However, the water knot remains essential for anyone making their own anchor material from webbing or for repair situations.
The water knot has one critical safety property: it can creep under cyclic loading. Webbing slings tied with water knots should be inspected regularly and the tails left long (at least 8 cm). Many fatal climbing accidents have been traced to water knots that crept until the tails pulled through.