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Abstract. The heating of drinking water in households contributes significantly to the emission of greenhouse gases. As a water utility aiming to operate at a climate neutral level by 2020, Waternet needs to reduce its CO 2 emission by 53 kton yr −1 . To contribute to this ambition, a pilot project was carried out in Uilenstede, Amstelveen, the Netherlands, to recover the shower heat energy with a shower heat exchanger from Dutch Solar Systems. An experimental setup was built in the Waternet laboratory to evaluate the claimed efficiencies. The energy recovery efficiency observed in the lab was 61-64 % under winter conditions and 57-62 % under summer conditions, while the energy recovery efficiency observed in Uilenstede was 57 % in December 2014. Based on the observations, 4 % of the total energy consumption of households in Amsterdam (electricity and gas) can be recovered with a shower heat exchanger installed in all households in Amsterdam, which also means a 54 kton year −1 CO 2 emission reduction can be achieved.

An inventory is made of the possibilities to recover sustainable energy from the water cycle by identifying different water flows in a municipal environment as a sustainable energy source. It is discussed what role public water utilities should play in the market of energy from water. This is done for Waternet, the public water utility of Amsterdam, by describing experiences on two practical applications for aquifer thermal energy storage and energy recovery from drinking water. The main conclusion is that public water utilities can substantially contribute to the production of sustainable energy, especially by making use of heat and cold from the water cycle. Public water utilities have the opportunity to both regulate and enter the market for energy from water.

Waternet, the public water cycle utility of Amsterdam and surroundings, has the ambition to operate climate neutrally in 2020. This requires a reduction of greenhouse gas (GHG) emissions of 48 kton CO 2 -eq. An inventory was made of measures to realize the target either in 2020 or in 2050. For all measures the effects on GHG emissions and on costs were determined. To comply with two core values of Waternet -economic effectivity and sustainability -the measures were prioritized based on CO 2 effectivity, defined as costs per ton GHG emission reduction. To realize the target in 2020, 34 measures have to be implemented. The total investments are € 60 million, while the measures result in a decrease in yearly costs of € 5 million from 2020 onwards. In the case where the target has to be realized in 2050, 10 measures have to be implemented with a total investment of € 100 million and a decrease in yearly costs of € 16 million from 2050 onwards. As the cumulative cost savings in 2050 are € 50 million higher for the case where the target is already reached in 2020, and the uncertainty is lower, the realization of the target in 2020 is preferred.

The heating of drinking water in households contributes significantly to the emission of greenhouse gases. As a water utility aiming to operate at a climate neutral level by 2020, Waternet needs to reduce its CO 2 emission by 53 kton yr −1 . To contribute to this ambition, a pilot project was carried out in Uilenstede, Amstelveen, the Netherlands, to recover the shower heat energy with a shower heat exchanger from Dutch Solar Systems. An experimental setup was built in the Waternet laboratory to evaluate the claimed efficiencies. The energy recovery efficiency observed in the lab was 61-64 % under winter conditions and 57-62 % under summer conditions, while the energy recovery efficiency observed in Uilenstede was 57 % in December 2014. Based on the observations, 4 % of the total energy consumption of households in Amsterdam (electricity and gas) can be recovered with a shower heat exchanger installed in all households in Amsterdam, which also means a 54 kton year −1 CO 2 emission reduction can be achieved.