DayCap In-Bottle FilterDESCRIPTION Youve already got your reusable bottle, now you just need the clean water. The DayCap In Bottle Filter from Platypus seamlessly fits onto three popular wide mouth water bottles Nalgene, Hydro Flask, and the Yeti Yonder transforming them into fast, safe and incredibly easy to use water filters. The removable filter utilises the same hollow fiber technology as their award winning backpacking filter systems to filter water safely and quickly.