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.

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To ensure delivery of microbiologically safe drinking water, the physical integrity of the distribution system is an important control measure. During repair works or an incident the drinking water pipe is open and microbiologically contaminated water or soil may enter. Before taking the pipe back into service it must be cleaned. The efficacy of flushing and shock chlorination was tested using a model pipe-loop system with a natural or cultured biofilm to which a microbial contamination (Escherichia coli, Clostridium perfringens spores and phiX174) was added. On average, flushing removed 1.5-2.7 log microorganisms from the water, but not the biofilm. In addition, sand added to the system was not completely removed. Flushing velocity (0.3 or 1.5 m/s) did not affect the efficacy. Shock chlorination (10 mg/L, 1-24 h) was very effective against E. coli and phiX174, but C. perfringens spores were partly resistant. Chlorination was slightly more effective in pipes with a natural compared to a cultured biofilm. Flushing alone is thus not sufficient after high risk repair works or incidents, and shock chlorination should be considered to remove microorganisms to ensure microbiologically safe drinking water. Prevention via hygienic working procedures, localizing and isolating the contamination source and issuing boil water advisories remain important, especially during confirmed contamination events.@en

Vrijwel alle drinkwaterbedrijven hebben ambities voor een klimaatneutrale bedrijfsvoering. Een aantal drinkwaterbedrijven probeert met opwekking van duurzame energie hun CO2-voetafdruk te verlagen. Een bijzondere manier van energieopwekking is de levering van thermische energie uit drinkwater, kortweg TED. Toepassing van TED moet een positieve milieu-impact hebben en de drinkwaterkwaliteit mag nooit in gevaar komen. Daarom is het voor drinkwaterbedrijven belangrijk om meer inzicht te krijgen in de risico’s van deze technologie. KWR Watercycle Research Institute heeft twee bestaande TED-systemen nader onderzocht op microbiologische risico’s, economisch rendement en milieu-impact (LCA). In dit artikel zijn de resultaten van het onderzoek kort samengevat.@en