Obtain Bernoulli’s equation of rest fluid.

Bernoulli's equation

$\mathrm{P}_{1}+\frac{1}{2} \rho v_{1}^{2}+\rho g h_{1}=\mathrm{P}_{2}+\frac{1}{2} \rho v_{2}^{2}+rho g h_{2}$

When fluid is rest, its velocity at every point is zero. In above equation $v_{1}=0, v_{2}=0$,

$\mathrm{P}_{1}+\rho g h_{1}=\mathrm{P}_{2}+\rho g h_{2}$

$\therefore  \mathrm{P}_{1}-\mathrm{P}_{2}=\rho g\left(h_{2}-h_{1}\right)$