North Water: Hydration Holster [Product ID: 30SK-20]
Fits all sizes from small 16 ounce (500 ml) to a one quart (litre) Nalgene™ bottle, insulated with built in floatation. Fits right or left of your deck and attaches to existing deck lines.
Can also be carried as a waist belt.
Product information and images courtesy of North Water.