Climate change demands for sustainable options for heating and cooling of buildings. Low-temperature thermal energy can be abstracted from the drinking water distribution system (DWDS); this is called thermal energy from drinking water (TED). The possible use of TED as a secondary function of the DWDS raises the question whether this secondary function can exist alongside the primary function (supplying safe and reliable drinking water) and, if so, under what conditions. Using various cases, the potential downstream effects of TED related to drinking water temperature (and hence, downstream increase of cost and CO₂emissions for water heating) and microbiological drinking water quality were studied.