If you want, you can incorporate
a built-in internal pocket for your water bladder (i.e. hydration system).
The given dimensions in figure 10 can accommodate a 2.5 L bladder. The
pocket itself is pleated at the bottom and has a top flap secured down
with hook and loop fasteners to keep the water container in place. It is
then sewn onto 1.0 oz nylon fabric with the same cut as the back/bottom
panel. This entire assembly is then sewn at the wrong side (inside) of
the back/bottom panel (photo 14).
To provide an exit port for the drinking
tube, cut a divot at the middle top edge of the back panel as shown in
figure 11. Next, fold the divot flaps inwards and sew flat at the folded
edges to form a sort of rectangular notch. Refer to figure 12 for a graphic
representation. Then cut a 3" x 1 3/4" piece of fabric similar to the back
panel and sew the short sides and a long side 1/4" inwards. These are the
so-called "finished edges". This will then be sewn over the notch to form
a shingle-like cover. Sew at the two short sides and at the long, unfinished
edge that coincides with the edge of the back panel. The unsewn long side
(finished edge) is where the hose exits. Photo 14 shows the water bladder
pocket assembly already sewn to the wrong side of the back/bottom panel.
The yellow stitch line (can you see it?) denotes the outline of the water
bladder pocket. Note the notch at the top middle edge where the hose exits.