As a reservoir for thirsty summers, we can store quite a bit of drinking water deep underground, according to a field study by drinking water company PWN in Hoorn. Between the sand grains and clay layers there is room for one billion liters of drinking water, a supply good for 21 days. “No sag or vibration is expected during inflation.”
In the municipality of Hoorn, drinking water company PWN has succeeded in retaining and recovering drinking water in a so-called ‘fresh water bubble’. Since 2020, the drinking water company has been working on constructing a water storage facility deep underground – located on the Leekerpad.
This is necessary because the drinking water supply in North Holland is becoming increasingly vulnerable due to thirsty summers, salinisation, housing and population growth.
Reason for field research in Hoorn
Roughly speaking, the eastern half of North Holland above the North Sea Canal receives drinking water that is produced in Andijk. There, water from the IJsselmeer is immediately purified into drinking water, which goes via a large transport pipeline to the pumping station in Hoorn – and from there further into the province.
If that transport pipeline fails – for whatever reason – there is another pipeline next to it that can take over the transport. “But it does have a more limited capacity, especially at peak times,” says Lucas Borst. He is a hydrologist at PWN.
Laying an extra pipe can be a solution, but there are also cheaper options. The test setup in Hoorn is particularly interesting because it is close to the pumping station, which limits the need for additional infrastructure. “By constructing a ‘fresh water bubble’ at the pumping station, from which we can pump drinking water during a pipe break, we have enough time to repair the pipe.”
The water storage can also be used ‘flexibly’. “If the system is built anyway, we can also use it on days with a high demand for drinking water. This way we are more resistant to droughts and we can also carry out better maintenance on our installations.”
One billion liters of drinking water
In recent years, the drinking water company has carried out tests thanks to a test setup with an extraction well. The preliminary results indicate that there is room to inject up to one billion liters of drinking water, at a depth of 50 to 100 metres.
Converted, that is almost 600 to 1,200 swimming pools of 25 meters. It is a water storage facility that is large enough to provide drinking water to about 200,000 North Hollanders for 21 days during the thirsty summer months.
No sagging or vibrations
Lucas Borst, hydrologist at PWN, is enthusiastic about the results that have been achieved. “The results are favorable and it is technically feasible, without any nuisance for the environment,” he assures. When inflating, according to Borst, there is no question of sagging and vibrations, a fear that reigns among some. “No one is waiting for damage, not even us as PWN,” he says. “The field investigation shows that no subsidence and vibrations due to inflation are expected.”
And will the stored water remain drinkable? Yes, Chest assures. “The quality of the water remains good in the soil. Because it is in the soil, under thick layers of clay, no contamination or pollution from the outside can occur.”
The drinking water company will make a decision in the autumn. If the test set-up is successful, the system will be expanded with ten extraction wells. PWN expects to be ‘fully operational’ around 2027/2028 – if all goes well.