When applying the widely-used Newton-Raphson (N-R) method to the integrated solution of the hybrid power-water flow problem of the power-water integrated energy system (PW-IES), it is found that there are numerical differences among Jacobian elements, which may yield an ill-conditioned Jacobian matrix and even cause convergence problem. Therefore, this letter proposes to per-unitize the water distribution network (WDN) to reduce the numerical differences and thus to improve the Jacobian matrix conditioning and the integrated N-R solution to the hybrid power-water flow problem.