Water in abundance, but a shortage of tap water looms

‘You see an abundance of water everywhere in our country,’ says Jan Peter van der Hoek, professor of water management and drinking water supply at the Faculty of Civil Engineering and Geosciences (CEG), when asked. “But of course, that report (in Dutch, eds.) hasn’t been published for no reason. Pollution, fertilisers, residues of medicines, pesticides and PFAS in groundwater and surface water are making it increasingly difficult to make water suitable for drinking. At the same time, we need more and more water. You might think that much of that pollution comes from abroad — after all, all those rivers reach their final destination here — but around 60% of the PFAS actually comes from the Netherlands itself.”

So, not good news. The report also shows that climate change and population growth are putting pressure on our drinking water. Longer periods of drought, combined with rising consumption, are placing an ever-greater strain on available sources. Van der Hoek: “So we need new sources. In doing so, we are also looking at alternatives, such as collecting and locally treating rainwater.”

Rainwater in Kerkrade

Rainwater from the tap: is that a solution? In the Bleijerheide neighbourhood in Kerkrade, residents collect rainwater and treat it locally. TU Delft is also contributing to that project. “A graduate student helped develop a monitoring plan for the water quality of such a system,” says Van der Hoek. “That is necessary, because drinking water must, of course, meet many requirements. Current Dutch and European regulations focus solely on groundwater and surface water. That is why we have mapped out how to monitor and guarantee the quality of rainwater, including a system description, monitoring parameters, measurement frequencies and analysis techniques. Data storage and analysis are also part of this. This will help in the future with the development of effective regulations.”

Rainwater storage

Isn’t rainwater clean by nature? That is a misconception, says Van der Hoek. “Air pollution, bird droppings on roofs, zinc leaching from gutters, oil and particulate matter on roads: you have to purify rainwater very thoroughly before you can drink it. What’s more, you need around sixty square metres of collection space per household. That’s simply not feasible, certainly in cities.” Does this mean that local rainwater systems have no future? According to Van der Hoek, that’s also too simplistic. “The smart collection and storage of rainwater can help in all sorts of ways.

‘The less polluted the water is, the more safely we can use it’

“At the Hortus Botanicus in Amsterdam, we are contributing to the design of such a buffer system. Researchers from CEG are working on water management, whilst the Faculty of Architecture and the Built Environment is involved in the design and spatial integration. Rainwater is collected and purified in the garden so that it can be used to water the plants. This saves a huge amount of drinking water. At the same time, it helps prevent flooding during heavy rainfall, as excess water is temporarily stored.”

Membrane filters

Using existing resources more intelligently thus helps to save drinking water, but demand for water continues to rise for the time being. Can’t we purify polluted water even more intelligently, for example using membrane filters? Van der Hoek: “Certainly, and that’s already happening. Drinking water companies such as Dunea and Brabant Water are already using such filters. They are so fine-meshed that they block virtually everything at a molecular level, except water molecules. Salts and minerals are then added back in later.”

However, there are also drawbacks to this technology. “Membrane filtration produces a residual flow of around twenty per cent that is five times as polluted as the original source. That is an enormous amount of polluted water that still needs to be treated further or discharged into surface water.”

According to Van der Hoek, the best solution therefore remains surprisingly simple: “We need to start at the source and take good care of our existing groundwater and surface water. The less polluted the water is, the more safely we can use it. There is still a great deal of potential for improvement in this area. We are also looking at alternative scenarios for water conservation, which involve a complete overhaul of the current distribution system for rainwater, greywater and the sewerage system. The current system has actually been inadequate for a long time now. More green and blue spaces in the city, rainwater that no longer disappears into the sewers but is collected separately, so that we can manage water more intelligently. That way, we’ll be well set for the future too.”

Text: Jaap van der Sar