In reaction A(aq)+B(aq)-->C(aq), where will the reaction shift if water is added and the concentrations are decreased? Will there be a shift?

If it is an irreversible reaction, i.e. A(aq) + B(aq) → C(aq)
there will not be any shift in equilibrium position.

If it is an reversible reaction, i.e. A(aq) + B(aq) ⇌ C(aq)
the equilibrium position will shift to the left when water is added.
In the equation, there are 2 moles of ions on the left and 1 mole on the right.
When water is added, the overall concentration of ions decreases instantaneously. According to Le Chatelier's principle, the equilibrium position will shift to the left to increase the concentration of ions.