It could be considered one of the most valuable goods known to man: water. It flows out of our taps every day, but where does it actually come from, how is it filtered, and who is responsible for maintaining the water network in Luxembourg? Here's a look behind the scenes.

RTL Today has teamed up with PISA, the Luxembourgish science magazine, to reproduce their original videos in English for our site. Presenter Olivier Catani takes you deep underground this week, as he dives into where our tap water comes from, and how it reaches us.

This video is part of the PISA series for RTL Today. Watch all English videos on RTL Play, or discover the wide range of subjects previously covered in Luxembourgish here (there are 13 seasons, mind you! We'll try and catch up...). Our previous episodes covered the history of the tramLuxembourg airport, explained how the coronavirus vaccine works and asked why traffic lights always seem to be red.

Water from wells, reservoirs and springs

A small part of Luxembourg’s tap water originates from wells. It can be pumped up 300 metres from below the surface. Rainwater drains into the ground, which is then filtered by the sandstone. At the bottom of this hard rock is an impenetrable layer where water builds up, and is then tapped into. To do so, they drill into the mountain horizontally so that no dirt from surface water can seep into the well.

The water generally has high levels of iron and manganate, because when the water sits at the base, the metals in the rock seep into the water. It’s not unhealthy per se, but has a very unique taste. At first it’s a little brown in colour, before being filtered.

Which water runs through whose taps depends on the location of their home. Some places funnel one sort exclusively, either reservoir, springwater or water from wells. Most communes provide a combination of several types.

The Grand Duchy’s tap water doesn’t always originate from water wells. A large share derives from the Upper Sure Lake. Works to erect the wall began in 1955. Back then it was considered the largest construction project in the country, towering 47 metres. The largest part measures four and a half metres thick. For the project, the state purchased 400 hectares of land, felling trees and constructing bridges and roads around the lake. A dozen homes were razed to the ground. Works finished in 1959, and one year later the lake was filled up.

Before water flows out the tap, a final quality check is completed in the lab. 250 parameters are checked, which include 50 different pesticides. Maximum levels must be observed. However, each day, thousands of litres of water fail the test. One could decide to clean the water, but it’s an expensive procedure, so it's funneled to water protection areas instead.