“Fui sobre agua edificada, mis muros de fuego son, esta es mi insignia y blasón (I was built upon water, my walls are fire, this is my insignia and blazon).” This motto for Madrid, engraved on the shields of Alfonso VIII of Castile’s militias, bore witness to the importance of the water beneath the city. The city’s name itself is derived from the Arabic Mayrit, which in the 11th century alluded to the many watercourses that flowed through the town. Until the Spanish Court arrived in the 16th century, Madrid only had water routes. This was a system to collect and distribute groundwater through a large network of galleries of Arabic origin (qanat, fogara, and jatara).
Underground, water is stored in geological formations called aquifers. Both the rainwater that flows in rivers and the water from floods or ice melts penetrates the ground, filling pores and fissures in the earth until it reaches impermeable layers that keep it from going farther down (known as the saturated zone). Under the city of Madrid, the water that inspired its name is in what we now call the tertiary detrital aquifer of the Madrid basin. This aquifer spans 2,600 square kilometres and was formed between 23 and 5 million years ago. It can reach almost 3,000 metres in depth, and the first 800 can be used for water supply. This is because the water is weakly mineralised and meets the parameters required for human consumption.
These underground ecosystems are some of the most extraordinary and least well-known on the planet. This is where tiny invertebrates and microorganisms live, adapted to life underground and a total absence of light. Groundwater sustains rivers and other associated ecosystems, supports agriculture, supplies a great number of towns, and fights the effects of climate change and drought.
According to the UNESCO, approximately 99% of all freshwater in liquid state belongs to the groundwater spread unequally all around the planet. This accounts for half the volume of water used in the household by the world’s population, and around one-fourth of all of it is used to irrigate 38% of all irrigation land in the world.
Groundwater ranks second worldwide as a freshwater reserve for the planet, behind polar ice caps and well ahead of lakes and reservoirs. In many countries, this is the main source of freshwater. In Spain, data from the Ministry for the Ecological Transition and Demographic Challenge (MITECO) estimate that around 30% comes from underground.
The presence of groundwater can guarantee supply for any population hub, provided that no more is extracted than it can recharge. In Madrid, the incorporation of groundwater into the autonomous community’s supply system, with 78 wells equipped with pumps that can extract water from a great depth, is a huge relief in terms of water management. This is because it provides a greater volume to contend with periods of drought or emergency situations.
In Spain, the MITECO estimates that nearly 40% of aquifers are in poor condition, mainly due to overuse and contamination. Climate change is also significantly reducing their ability to naturally recharge, and rising sea levels are causing more and more issues with seawater intrusion into certain coastal aquifers.
Due to all the aforementioned, in addition to sustainably managing this underground resource to guarantee quality and availability, it is important to implement innovative solutions like the LIFE Matrix project. This pilot project, funded by the European Union, is testing a system for “managed aquifer recharging” with regenerated water. It aims to increase groundwater resources by 15%, all while reducing power consumption and greenhouse gas emissions as opposed to other technologies. The population’s growing needs increase demand for groundwater. This resource is vast and vital for our lifestyle, but it is limited and needs to be used sustainably. This is why “making the invisible visible“ is so important, as pointed out by the United Nations slogan for World Water Day 2022.
