Rainwater for toilets and washing machines saves electricity and reduces the need for cleaning

The treatment plant in Nye that purifies rainwater from roofs, roads, and squares, and sends it to toilet tanks and washing machines in households. The plant is equipped with advanced purification technology, which ensures that the water does not discolour the clothes. Illustration: Aarhus Vand

Reclaimed water has been a controversial phenomenon for decades. Is it really worth it to collect water from surfaces and drains, purify it, and use it in toilet tanks and washing machines? Water utilities want to save on the scarce resource of groundwater, but can other inconveniences arise?

DTU Environment has now analysed the supply of reclaimed water in the new “sustainable” Aarhus district Nye and brought us a little closer to the answer.

“There is no conclusive result, but in three important areas, there is no doubt that the solution with reclaimed water is sensible in terms of sustainability,” says Maria Faragò, who has carried out the life-cycle assessment at DTU Environment.

Soft water saves energy and cleaning products

In Nye, all rainwater and surface water is collected in a number of lakes, which also act as climate proofing for extreme weather events. In addition, water is collected from drainage pipes at houses and roads. The two types of water are treated in a separate treatment plant.

Since there are no standards for this type of reclaimed water yet, and its use in washing machines requires that the water does not contain allergenic substances, it is purified to a quality almost equivalent to drinking water. For consumers, the price per cubic meter is the same as for drinking water. But they can in turn save on other things.

“Firstly, the solution leads to savings in groundwater. In addition, rainwater is much softer than groundwater. This means that consumers save on electricity and cleaning products by not having to descale their washing machines as often,” Maria Faragò explains.

Only cost-efficient in new developments

Project Manager Kristian Brunmark at Aarhus Vand, the utility which has established and operates the reclaimed water solution, believes that the life-cycle assessment is very valuable.

“We would be reluctant to introduce a dual piping system in the new district if the assessment had indicated that it did not make sense in terms of sustainability. Especially because this is only the first stage of the new district, which needs to be expanded further in the coming years. The experience with the reclaimed water supply in the first stage will of course come into play,” he says.

In Nye, 600 homes have been built in the first stage, but in the long term, the district will house approx. 15 000 inhabitants.

The developer believes in the value but has not crunched the numbers

For Jørn Tækker, whose company Tækker Group owns and is developing the entire district, the rainwater recycling means that an additional water pipe must be installed in all homes and an additional meter must be set up. In addition, Tækker Group has set some rules for the use of pesticides in the gardens, and the company is responsible for winter maintenance.

“We have made an agreement with Aarhus Vand that we will supply rainwater to the lake from which the treatment plant draws the water. Therefore, we have banned the use of pesticides in the gardens, and we are responsible for winter maintenance of the roads, because if we left it to Aarhus Municipality, they would use road salt, which would make the purification process much more expensive since the salt must be removed. Instead, we use gravel and crushed rock—which must not have been dug up from the sea, because then they would also contain salt. But it does not cost a lot more,” he says.

He has not calculated how much additional pipes, meters, and winter maintenance cost, but he is sure that in the long run, it is a good investment—financially as well.

“Of course, it costs more to install two pipes instead of just one. On the other hand, 40 percent of the groundwater resources are saved, and the residents save on electricity and detergent for the washing machines. And there are actually a lot of people who opt for that. So I believe that building something that is good for nature, for the environment, and for consumption leads to more home sales and a more differentiated potential group of buyers,” he explains.

Hope to replace all groundwater with reclaimed water

In the long run, however, it may be that the solution can be made a little cheaper by settling for one water pipe and one meter. Jørn Tækker hopes that his original vision of virtually eliminating groundwater consumption can be realized.

“There is enough rainwater to cover the water consumption of the entire district. But as the rules are today, drinking water cannot be replaced with purified drinking water, even if it is just as clean as groundwater—or in fact even more clean once we have purified it. We are measuring and recording the water quality, and we hope that we can change the legislation with enough experience.”

If purified reclaimed water gets the same status as drinking water, the argument for requiring separate piping for the reclaimed water disappears—and with that also the extra cost that may hold back some developers.

But even without this legislative change, developers should be interested in reclaimed water recycling. Politicians and officials from several municipalities have visited Nye to see if they should replicate the concept.

Other municipalities are also interested

According to Brunmark, other municipalities have shown interest in the solution with a dual piping system. However, he emphasizes that the solution is only interesting in connection with new developments, as it would be too expensive to install an additional set of pipes for reclaimed water in existing buildings.

The same been pointed out by e.g. Rambøll. The consultancy firm has assessed the price as the most limiting factor, as the construction costs most often exceed the water savings during the lifetime of the installations.

The assessment was conducted with the relatively small amount of data available at present. Once the system is in operation for a year, DTU Environment and Aarhus Vand hope to be able to update the assessment with the real figures from the operating period.