  Urban water networks can contribute to the energy transition of cities by
serving as alternatives sources for heating and cooling. Indeed, the thermal
energy potential of the urban water cycle is considerable. Paris is taken as an
example to present an assessment of the field performance of a district-scale
waste water heat recovery system and to explore potential techniques for
emergency cold recovery from drinking or non-potable water networks in response
to heat-waves. The case heat recovery system was found to provide significant
greenhouse gas emission reductions (up to 75%) and limited primary energy
savings (around 30%). These limited savings are found to be mainly due to the
performance of the heat pump system. Three emergency cold recovery techniques
are presented as a response to heat-waves: subway station cooling, ice
production for individual cooling, and "heat-wave shelter" cooling in
association with pavement-watering. The cold generation potential of each
approach is assessed with a special consideration for mains water temperature
sanitary limitations. Finally, technical obstacles and perspectives are
discussed.
