The ornamental design for an waterbottleholder, as shown and described.
FIG. 1 is a perspective view of a water bottle holder in situ secured to an associated horse jump post;
FIG. 2 is a perspective view thereof in situ unmounted;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a first side view thereof;
FIG. 6 is a second side view thereof; and,
FIG. 7 is a third side view thereof.
The broken lines showing the holes and knob in the water bottle holder are unclaimed. The remaining broken lines showing the bottle, equestrian hitching post, tether and pin are for illustrative purposes only and form no part of the claimed design.