The period wlll decrease - it will swing faster
The period of a simple pendulum is just
P = 2 π √(L / g)
However, with a compound pendulum one must also consider the moment of inertia about the center of mass at distance L.
As water drains from the sphere its moment of inertia about its point of suspension will decrease and the pendulum will swing faster
Technically P = 2 π √I0 / M g L)
where I0 = M L^2 + Icm Icm is moment of inertia about the center of mass - if Icm = zero then P = 2 π √(L / g) the simple pendulum