The 1/4" Cut Off valve is used to shut off the product water after the RO system. Two of these John Guest fittings are included with every RO system.
Note: This fitting is threaded to fit on a bladder tank, but for water collection that won't matter. Press fitting onto the blue tubing, and open valve over container of choice. Close valve when done, and RO system will shut off within 60 seconds when system repressurizes internally.