Water Sector

Keeping a safe distance between water mains and heating networks

With the energy transition, particularly in large urban areas, underground water mains and heating networks are getting closer together all the time. But what distance has to be maintained to ensure the drinking water doesn’t get too warm? The ENGINE project has supplied knowledge and practical tools to answer this question. And that is very much needed given the social interests at stake, thinks Casper Jansen of Vattenfall.

“It’s not just about maintaining our ability to guarantee safe drinking water. We also have to achieve the climate goals at an acceptable cost.”

The Dutch drinking water companies and the heating companies teamed up to address the joint challenge of meeting society’s need for safe and healthy drinking water, and implementing the energy transition. The result was the ENGINE TKI project, which was completed recently. The aim of ENGINE was to develop insights and tools to determine how space can be made below our streets for both heating networks and water mains without making drinking water too warm. It developed validated models which can be used to tighten up the current standards.

Shortage of space below the surface

Jansen outlines the challenge from the perspective of the heating companies. “We are in the middle of the energy transition. It’s something we are working on every day. In urban areas, for example, we are working on the roll-out of heating networks, which use residual heat from industry, geothermal energy and heat pumps, for example. What we are seeing is a shift from connecting new homes – in which the quality of insulation is getting better all the time, meaning that they require less and less heating – to disconnecting existing buildings from the gas supply and connecting them to a heating network. Particularly in large urban areas, it is difficult to find the space for all this below the surface. As a result, heating and water companies are increasingly being forced to install their pipelines in closer proximity to one another. In specific situations, we have to use specialist consultancy firms to look at what can, or cannot, be done. That takes a lot of time and money, which is why we thought the ENGINE project could provide a solution.”


The development outlined by Jansen is confirmed by Joost Louter, who works for Waternet. Like Jansen, Louter was a member of the ENGINE core team and he was also involved in the preliminary stages of this project.

“In addition to the increase in heat sources in the subsurface, we also have climate change,” says Louter.

“And so we expect drinking water to warm up in the future, while the Drinking Water Act doesn’t allow us to exceed 25°C. It is vital to make clear what our options are here, and how much warming is involved. We couldn’t do that in the past because everyone was making their own calculations using different assumptions. But ENGINE has now established the basis for a national approach with validated models. There is consensus about the results at both the drinking water and heating companies.”

Two models

Two models were developed in the ENGINE project to establish the desirable minimum distance between heat sources and drinking water mains. One was a soil temperature model developed by Deltares; the other was a water temperature model developed by KWR. The models were validated with measurements made in practice and then they were used to calculate a number of scenarios with tables of exceedance probabilities. Louter explains: “Of course, the drinking water companies do not want to block the energy transition. We will not be manning the barricades to defend the 25-degree limit at all costs. The point is to determine an acceptable risk for warming. As a general rule, we prefer if it heating networks have no effect at all on water mains. So if the space is available, the two networks should be on different sides of the street. But if there is no other option, we accept an exceedance probability of no more than one degree in x percent of households. Our guiding principle when it comes to determining the value for x is that drinking water and heating companies should give each other room so that we can all do our jobs.”

National standard

The two sectors still have to agree on an exact value for the acceptable exceedance probability for warming. So Jansen emphasises that the desired result hasn’t been achieved yet. “The scope of the research doesn’t include a recommended distance between heating networks and water mains. In my experience, the water sector wants more of a safety margin, while the heating companies prefer to sail closer to the wind. Our advice is to minimise the distance in a responsible way. That provides most flexibility. To move forward, it is vital for us to follow through, and to determine the national standard that should emerge from the research results. That is why the heating and drinking water companies are working together to incorporate ENGINE’s results in NEN 7171, the standard that defines the planning of underground networks. Our people can get to work only once that has been done. I think that this next stage will be the biggest challenge. It will be quite a job to determine the require distances in a healthy dialogue. But I have every confidence we can get it done. If we do not take the opportunity now, there will simply be no standard. And then we will have to negotiate time and again because nothing will be clearly defined. That is not an option.”

Shortage of space below the surface: the ENGINE project brings together knowledge and tools to determine the required minimum distance between heat sources and water mains.

Establishing the conditions

The urgency of establishing a standard is also clear to see at the drinking water companies, Louter says. “Even though we are already seeing warming in the mains, there are almost no signs of it in people’s homes. We are still at a preliminary stage. But once the energy transition gets going properly, so many heating networks will have to be built that you won’t have any more opportunities to set up the regulations properly. We have to establish the conditions now so that we won’t run into problems in the future, because then there won’t be any room for manoeuvre. Just imagine: if we fail to sort out those conditions in time, we may have to use chlorine in drinking water again. Obviously, that’s out of the question.”

Connecting water and energy

All in all, the conclusion is that ENGINE has been a success in terms of connecting the energy and water sectors.

“We were able to team up through TKI at the national level,” Louter says.

“There is openness from both sides about the challenges that lie ahead. We are also working in partnership at the sector level with VEWIN and Energie-Nederland, the respective branch associations for the water and energy sectors. I do think it is unfortunate that the grid operators failed to join ENGINE. They had done so in the earlier stages. Warming in the subsurface is also an issue for them. In addition to standardisation, an important next step will be to engage with municipal authorities. Their agendas also need to include the warming up of drinking water alongside issues relating to problems with rainwater and habitability, now and in the future. The ENGINE results help to visualise these areas, for example in heat stress maps. With the right basis, we can help to design public space much better.”

The TKI project ENGINE: Energy and Drinking Water in Balance was implemented by a large consortium consisting of: Deltares, KWR, Brabant Water, Dunea, Evides, Oasen, PWN, Vitens, Waterbedrijf Groningen, Waternet, WMD Drinkwater, Waterleiding Maatschappij Limburg, Energie-Nederland N.V., Nederlandse Gasunie, and Convenant Samenwerken in de buitenruimte, an alliance of the City of Rotterdam, Stedin and Evides.