Remove tiles from your garden, put in plants, lay a green roof … These are all measures that people can take themselves for a greener, cooler and ‘more climate -resistant’ garden. Another frequently mentioned measure is the ‘disconnection’ of your rain pipe. Normally rain pipes lead the water from your roof to the sewer. If you disconnect the rain pipe, the water goes to a rain barrel, or directly to your pond or garden. Does that put that on? Or is it a drop on a glowing plate?
There are two reasons to disconnect your rain pipe, says Paulien van der Geest of the Environment Central Information Organization. “If you combine the disconnection with placing a rain barrel, you can give your garden rainwater instead of drinking water. Now, Dutch garden owners use on average around 1,100 liters of drinking water to spray the garden every year, often in dry periods when drinking water deficits threaten.”
An average household uses such an annual 100,000 litersso the no spraying of the garden saves roughly 1 percent of the total water consumption. Is that much? Relatively not, but in an absolute sense: there are around 5.5 million gardens in the Netherlands.
Sewerage load
There is a second important reason to disconnect your drainpipe, says Van der Geest: “It ensures that rainwater no longer flows into the sewer. The clean rainwater is not purified unnecessarily and the sewer runs less quickly. That is becoming increasingly relevant, now that climate change is increasingly confronted with more precipitation and hoosbuien.”
But how much rain is actually on our roofs? Is that really a big load on the sewer? We ask Leon Droppert from consultancy and engineering firm Tauw. “On average, roughly 800 millimeters of precipitation falls annually,” he says. “Based on an average of 60 square meters of roof surface, this is almost 50,000 liters of clean rainwater per household that flows through the roofs to the sewerage and therefore the sewage treatment. The cancellation of the rain pipes can therefore reduce the total private load of the sewer system with approximately a third, compared to the 100,000 liters of waste water but all the fact.”
Rain, however, does not only fall on the roofs in built -up areas. It also falls on the sidewalks and streets, and then ends up in the sewer. Hilde Niezen from the Rioned Foundation, the “umbrella organization for good care for waste water, rainwater and groundwater in towns and villages,” knows more about that. “The Dutch municipalities are installing separate sewers,” she says. “One sewerage for waste water and one for rainwater, especially to prevent mixing with waste water and overload, and to retain rainwater locally. This is becoming increasingly relevant due to climate change. With new construction, separate sewerage is now the standard, and many municipalities nowadays disconnect the rainwater as existing sewerage has to be replaced.”
Sneezing refers to the Municipal water tasks monitor 2024. “In total there is 163,000 kilometers of sewerage in the Netherlands,” she says. “There is 1,800 million square meters of paved surface in cities and villages: roofs, roads and tiled gardens. Of this, 49 percent are connected to mixed sewerage. About 15 percent is retained in verges, wadis or ditches and infiltrates to the groundwater. For the other 36 percent, separate sewerage has been laid there.”
To ditches or rivers
That often goes directly to ditches or rivers. Niezen: “Often there is a facility to drain the water from small showers to the purification: it contains a relatively large amount of street waste, including microplastics and soot from car tires.”
Part of the water that falls on the paved surfaces evaporates or sinks in joints. In the end, around three -quarters of the water that falls on all paved surfaces comes to the sewage treatment, Niezen charges. The overload problem is therefore a quarter smaller than you would think at first sight- and it will decrease further as municipalities create more separate sewers, plus water collection and infiltration facilities.
Then the question remains how the roof water relates to street water. With an average Dutch roof surface of 60 square meters and 8.4 million households We come to very roughly 500 million square meters of roof surface – so 28 percent of the total paved surface that is connected to the sewer system. Three quarters of this is the profit that can be made if you disconnect all those roofs.
And how many garden owners are their rain pipes already linking? “Sun 37 percent It is that they have done it, in our representative research among 1,005 Dutch garden owners, “says Paulien van der Geest of Milieu Centraal.” But sometimes there is a difference with actual behavior. Anyway there is still plenty to discover. And there is often a subsidy for that. “