The management of energy-water nexus in buildings is increasingly gaining attention among domestic
end-users. In developing countries, potable water supply is unreliable due to increasing demand, forcing
end-users to seek alternative strategies such as pumping and storage in rooftop tanks to reliably meet
their water demand. However, this is at an increased cost of energy cost. In this paper, the open loop optimal
control model and the closed-loop model predictive control (MPC) model, both with disturbances,
are compared while minimizing the maintenance cost of the pump. The open loop optimal model is suitable
in instances where only random disturbances due to measurement errors are present. However, in
case the demand pattern changes for reasons such as occupancy change in the house, the closed-loop
MPC model is suitable as it robustly minimizes the pumping cost while meeting the customer demand.
Further, MPC proves its robustness as it is able to overcome the turnpike phenomenon. Each of these two
models has their own strengths. The open loop model is cost effective and easy to implement for customers
that have a steady demand pattern while the closed-loop MPC model is more robust against
demand pattern changes and external disturbances. It is recommended that these two models are
adopted according to the specific application.