Large-scale integration of renewable energy sources with their intermittent output is introducing new challenges for system operators. The challenge arises from imperfect wind and solar forecasts that lead to deviations in electricity production in real time. This has urged system operators to explore new sources of flexibility including the water sector. Along with these advancements, municipalities are becoming increasingly interested in coordinating water and energy systems in urban areas. This study introduces a novel market-based mechanism for harnessing flexibility from an integrated water and power system. The mechanism is formulated as a data-driven distribution robust chance-constrained program. It coordinates the operation of flexible power generators and water pumps through affine policies, regulating the participation of flexible assets in day-ahead and real-time market segments. Water flows are approximated through a novel convex hull-based relaxation technique. This results in a second-order cone program that allows the power system operator to leverage demand-side flexibility from the water network. The fluctuating water demands, derived from direct consumption measurements, are considered to ensure seamless integration with renewable energy sources. The water distribution network is explored for its potential to offer flexibility services, such as demand response to the power network. The mechanism is tested on a real case study in Alicante, Spain, to determine effective water-energy regulation policies and identify potential cost savings. Read more here: https://ieeexplore.ieee.org/abstract/document/10562284