  This paper formalizes an optimal water-power flow (OWPF) problem to optimize
the use of controllable assets across power and water systems while accounting
for the couplings between the two infrastructures. Tanks and pumps are
optimally managed to satisfy water demand while improving power grid
operations; {for the power network, an AC optimal power flow formulation is
augmented to accommodate the controllability of water pumps.} Unfortunately,
the physics governing the operation of the two infrastructures and coupling
constraints lead to a nonconvex (and, in fact, NP-hard) problem; however, after
reformulating OWPF as a nonconvex, quadratically-constrained quadratic problem,
a feasible point pursuit-successive convex approximation approach is used to
identify feasible and optimal solutions. In addition, a distributed solver
based on the alternating direction method of multipliers enables water and
power operators to pursue individual objectives while respecting the couplings
between the two networks. The merits of the proposed approach are demonstrated
for the case of a distribution feeder coupled with a municipal water
distribution network.
