How to get pressure from continuity equation for an incompressible fluid? The initial formulation of continuity equation for in-compressible fluids does not contain initially pressure. 
$$\nabla \cdot \vec v = 0$$
I have seen, in some books it is assumed that pressure is calculated from continuity equation. How can we get such a relation from continuity equation which does not contain pressure initially?
The author calls such a formulation of continuity equation -from which we get pressure- as 'primitive variable formulation'. 
 A: You solve two equations: continuity and Navier Stokes equation, to find two unknowns: velocity vector field and (scalar) pressure field. Solving only Navier Stokes equation gives you velocity field as a function of pressure. Then the pressure field must be such that the resulting velocity field satisfies continuity equation. This is what is meant when one says that pressure is to be found from continuity equation.
A: In the limit of an incompressible fluid, you get the pressure from a combination of the incompressible continuity equation and the boundary conditions for the system.  For example, at a free surface, the pressure is equal to the externally applied pressure from the adjacent medium.  In flow in a pipe discharging to the atmosphere, the downstream pressure is atmospheric, and the upstream pressure is higher than atmospheric by whatever amount is necessary to provide the required flow rate.  In carrying out this calculation, the continuity equation provides a constraint which tells you that the volumetric flow rate is constant, independent of axial position.  
