How the Network That Cleans Water in the Balearic Islands Works

Few infrastructures are as hidden yet, at the same time, as essential as those that purify water. In an island region with limited aquifers and rising pressure from tourism, proper wastewater management is more than just an environmental requirement: it’s a vital necessity. ABAQUA, the Balearic Water Agency, is in charge of ensuring this system works every day. From pumping stations to large wastewater treatment plants, its network turns wastewater into a clean resource, thereby protecting the sea, the soil and public health.

It all starts under our feet. The sewer system collects used water and carries it to the main collectors. This is where ABAQUA comes into play, which manages what’s known as the “bulk” or main network: pumping stations, large pipelines and, finally, treatment plants—the so-called WWTPs. There, the water is cleaned before being returned to the environment or reused. It may sound mundane, but without this gear, the beaches, streams and marine ecosystems would be at risk.

The process is carefully coordinated. First comes the pre-treatment, where screens and desanders filter out wet wipes, plastics and other large particles. This is followed by biological treatment: millions of microorganisms work in aerated tanks to break down organic matter. This is the living part of purification, where science imitates nature. The sludge is then separated from the clean water. If the water is to be reused (for example, to irrigate green spaces or farmland), the water undergoes tertiary treatment to achieve high-quality water that meets the highest standards.

In the meantime, the resulting sludge continues its own journey: it undergoes thickening, digestion and dewatering before final disposal. Nothing is improvised: everything is measured, controlled and automated to ensure that not a single drop goes back into the environment without proper treatment.

The scale of the system is enormous. ABAQUA manages 79 wastewater treatment plants across the four islands, capable of treating more than 50 cubic hectometres of wastewater per year. In summer, demand soars: tourism increases the population and the plants run at full capacity. In winter, less demand means maintenance and improvements can take place. This constant balance between anticipation and response keeps the system running non-stop.

The quality of the treated water is monitored on a daily basis. The WWTPs analyse parameters such as biological and chemical oxygen demand to ensure that the outgoing water meets EU standards. The balance is positive: almost all plants in the Balearic Islands exceed quality standards. The few with problems are now being replaced or expanded, such as the old wastewater treatment plant in Ibiza. In its place, the new Vila facility, co-financed by the Spanish government, promises to put an end to years of problematic discharge and mark a new approach.

But it’s not only about the treatment plants. The challenge also lies in the water coming through the sewers. In some coastal municipalities, saltwater intrusion and outdated networks mean incoming wastewater has a high salt content, which complicates treatment and limits reuse. Industrial discharge and brine from private desalination plants also affects the quality of incoming water. For this reason, ABAQUA is working closely with local councils to upgrade pipes, separate rainwater and control discharge: a modern wastewater treatment plant is useless if the incoming water is polluted from the outset.

Meanwhile, the agency is leading expansion and modernisation projects in municipalities with the highest population growth. Inca, Consell and Felanitx, for example, have renovation plans in place so they can adapt to a much higher volume of wastewater than a decade ago. The goal is clear: to prevent overload, improve performance and provide for future needs.

And while the work of a wastewater treatment plant seems purely technical, it can also be an environmental opportunity. ABAQUA, in collaboration with WWF, is implementing a biodiversity plan that’s turned the evaporation ponds of 28 wastewater treatment plants into real natural oases. Species of aquatic bird species nest there, including the common coot and great crested grebe, having found a safe refuge in these fresh water bodies in the inner parts of the islands. A clear example of how man-made structures can support other living things.

Looking to the future, ABAQUA is committed to digitalisation and energy efficiency. Remote-control systems allow real-time monitoring of water flows and processes, and the inclusion of renewable energy will reduce amount of electricity used by the plants. The reuse of treated water, the use of sludge and the improvement of the coastline are helping to create an increasingly circular model.

The result is a closed loop that completes the water cycle. What was once considered waste is now a resource. Every litre properly treated means less pollution, less pressure on aquifers and a better future for a region that depends on the delicate balance between development and sustainability.

In the end, behind every drain is a story of engineering, science and public service. A system that may not be visible, but which makes it possible to return clean water to the sea, the ground and living ecosystems. For islands that thrive on water just as much as they do on the land, this is perhaps the best example of everyday sustainability.