If the fluid is assumed to be incompressible (Note: Normally it implies that the volume is incompressible) then the qontinuity equation become in recatngular coordinates:
or
Note: this equation is good for unsteady incompressible flows and the density
may be constant or may not be constant. Subtracting the above equation
from the full equation we have
Cylindrical Coordinates:
Spherical Coordinates:
