You need the Eulerian equation for ideal fluid:

,where is the fluid density, is the volume density of mass forces( in case of gravity), is the pressure gradient.

Other forms: (Refer Wikipedia)

ρis the fluid mass density,is the fluid velocityvector, with componentsuu,v, andw,E = ρ e + ½ ρ ( u2 + v2 + w2 )is the total energy per unit volume, witheis the internal energy per unit mass for the fluid, andpis the pressure.