A new domestic hot water strategy reduces energy demand and operating costs

ETH Zurich will reduce the number of domestic hot water supply networks and water outlets in its buildings. This will lower energy demand and operating costs while maintaining the high level of water hygiene already in place.

09.12.2025 by Engineering and Systems department

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This autumn, ETH Zurich made an important decision regarding domestic water supply. By adopting a new strategy for domestic hot and cold water systems, the university is tackling issues relating to high energy costs, energy efficiency, sustainability (net zero targets) and water hygiene.

“Consistently implementing the new strategy for domestic hot and cold water systems will improve the energy efficiency of our buildings and help us to achieve our net zero targets in the long term.”
Dario D'Ercole, Head of Building Technology and Energy, Engineering and Systems Department

The strategy outlines an approach that aims to solve two problems. Firstly, an extensive supply network with numerous rarely used water outlets causes stagnation and thus impairs water hygiene. With fewer water outlets and a smaller supply network, it will be easier and more cost-effective to maintain the high level of water hygiene that is currently achieved. In particular, the risk of Legionella will be significantly reduced.

Secondly, extensive domestic hot water networks substantially increase energy demand, as water must be maintained at high temperatures at all times to meet hygiene standards. This alone accounts for roughly 20 percent of a building’s total energy demand. The new strategy will largely eliminate this requirement.

Decentralised water heating

In future, water outlets will only be installed where necessary, for example in toilets and kitchenettes. Centrally supplied hot water networks will normally be eliminated completely. While domestic hot water will still be provided, it will only be supplied where it is required in accordance with standards and user-specific processes, such as in showers and barrier-free toilets.

Decentralised solutions will be preferred for heating water, for example using tankless (instantaneous) water heaters. This will allow significant savings to be made on piping and maintenance costs. Where possible, showers will be centralised within a building area and their number will be reduced. In addition, legal requirements will be implemented, such as replacing electric hot water storage tanks larger than 60 litres ("electric boilers") with decentralised solutions.

“Decentralised water heating with instantaneous water heaters is more energy-efficient and reduces pipe losses, while ensuring that our high standards of water hygiene are met.”
Simon Wepfer, Head of Service Building Management, Facility Services Department

Implementation as part of renovation projects

The new strategy for domestic hot and cold water systems is being implemented in all new buildings. Many ongoing construction projects are also taking the strategy into account. In existing buildings, the strategy is being implemented gradually, as part of renovations, replacements or planned maintenance work.

The new specifications apply to ETH Zurich buildings. For rental properties, the domestic water strategy is always agreed with the owner.

“In existing buildings, the infrastructure will only be replaced if a renovation is already planned or necessary. The new approach to domestic hot and cold water systems will then be implemented directly.”
Catharina Weis, Project Manager, Real Estate Management

Great potential for optimisation

Existing buildings offer significant opportunities for energy and financial optimisation if the operating costs over the subsequent average service life of 40 years are considered alongside the investment cost of a future renovation (see chart).

Diagram with six columns. There are two columns for each of the three ETH buildings HG, ETZ and CLA. These two columns show the investment and operating costs over the life cycle, once for the conventional approach and once for the new strategy. There are no major differences in investment costs. However, with the new strategy, the operating costs for all three buildings are significantly lower than with the conventional approach. — The chart shows estimated investment costs for a future water heating renovation (dark) and subsequent life-cycle operating costs (light) for three exemplary ETH buildings (HG, ETZ and CLA). The estimated investment costs for a renovation with conventional central water heating differ only slightly from the cost of a decentralised solution in accordance with the new strategy. However, there are significant differences in the operating costs over an estimated life cycle of 40 years. The comparison takes into account the removal costs for the decommissioned hot water pipes and the replacement costs for instantaneous water heaters. Cost estimates in CHF. (Chart: ETH Zurich)

Further information

Efficient use of energy

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