A Water Knot (also called a Tape Knot, Ring Bend, Grass Knot, or Overhand Follow-Through) is a knot frequently used in climbing for joining two ends of webbing together, for instance when making a sling.
To Tie a Water Knot:
Tie a normal overhand knot, leaving at least a 6 inch tail. Make sure the webbing is flat, not twisted.
Insert the other end of the webbing where the tail comes out.
Follow the webbing around the knot.
Go back through the knot to the other side so you have tails sticking out both sides of the knot.