A flow control mechanism is provided for regulating the flow of fluid from a container or vessel, e.g., a plastic bottle containing a fluid such as water or the like. The flow control mechanism may be advantageously employed in a variety of applications where it is desired to dispense and/or access fluids in a controlled manner, e.g., applications wherein a liquid, colloidal system, suspension or the like is to be dispensed/accessed in a controlled manner. The flow control mechanisms are particularly advantageous as animal/pet drinking aids that provide animals/pets with convenient and controlled access to fluid refreshment, e.g., when away from a home-based water bowl. An exemplary control mechanism includes a cap member, overcap and ball captured therebetween. The cap member may be secured to a fluid-containing vessel and used to regulate or control the flow of fluid therefrom. In an alternative embodiment, the overcap defines an angular geometry and a pair of balls are positioned therewithin. A dual fluid vessel is also provided for use with the foregoing control mechanisms.