Can water in conduit cause an increase in voltage?
Voltage at the inverter's output needs to be greater than grid voltage if the current has to flow into the grid. It depends on grid impedance how much this voltage will rise for the same current. Simple ohms law : U=R*I can be writen as (Uinverter-U_grid)=I_inverter * R_grid, then Uinverter = I_inverter * R_grid + U_grid. It is prety trivial that voltage rise will be greater if grid impedance is larger (long distance to the transformer or small wires cross section).
As long the voltage rise is in the tolerance (approx +10%) the inverter will not limit the output voltage. If the voltage is limited, then the system cannot deliver the full available power from PV array.