FIG. 1 is a perspective view of a hydration reservoir with a cap tether shown not in use;
  
    FIG. 2 is a top view of the hydration reservoir of FIG. 1;
  
    FIG. 3 is a bottom view of the hydration reservoir of FIG. 1;
  
    FIG. 4 is a right side view of the hydration reservoir of FIG. 1;
  
    FIG. 5 is a left side view of the hydration reservoir of FIG. 1;
  
    FIG. 6 is a front view of the hydration reservoir of FIG. 1;
  
    FIG. 7 is a rear view of the hydration reservoir of FIG. 1; and,
  
    FIG. 8 is a perspective view of the hydration reservoir of FIG. 1 with the cap tether shown in use and attached to the cap.
  The dashed lines in FIGS. 1 through 8 illustrate portions of the hydration reservoir and form no part of the claimed design.