It depends on the nature of the chemical.
(a) If the solution contains a weak base and its conjugate acid
The solution is a buffer.
Its pH will not change on the addition of water because the relative concentrations of the acid and its conjugate base do not change on dilution.
(b) If the solution contains a strong base
If you dilute 4 oz of the solution with 1 gal (128 oz) of water, the new concentration is
The pH will decrease to 9.9.